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THE  LIBRARY 

OF 

THE  UNIVERSITY 

OF  CALIFORNIA 

LOS  ANGELES 


GIFT  OF 

John  S.Prell 


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WORKS  OF 
PROFESSOR  CECIL  H.  PEABODY 

PUBLISHED    BY 

JOHN  WILEY  &  SONS. 


Thermodynamics  of  the   Steam-engine  and  other 
Heat-engine*. 

Tins  work  is  intended  for  the  use  of  students  in 
technical  schools,  and  gives  the  theoretical  training 
required  by  engineers.  Sixth  Edition,  Revised. 
vii  +  543  pages,  119  hgures.  8vo,  cloth.  $5.00. 
Tables  of  the  Properties  of  Steam  and  other 
Vapors,   and  Temperature=Entropy  Table. 

These  tables  were  prepared  for  the  use  of  students 
in  technical  schools  and  colleges  and  of  engineers  in 
general.  Eighth  Edition,  Rewritten.  8vo,  vi  +  133 
pages,  cloth,  $1.00. 

Valve=gears  for  Steam-engines. 

This  book  is  intended  to  give  engineering  students 
instruction  in  the  theory  and  practice  of  designing 
valve-gears  for  steam-engines.  Second  Edition, 
Revised  and  Enlarged.  8vo,  v-f- 142  pages.  33  f<  Ici- 
ing-plates,  cloth,  $'J  50 

Steam-boilers. 

By  Prof.  Cecil  H.  Peabodv  and  Prof.  Edward  F. 
Miller,  viii -1-434  pages;  175  illustrations.  8vo,  cloth. 
$4.00. 

Manual   of  the  Steam-engine  Indicator. 

154  pages;  98  figures,     l2mo,  cloth,  $1.50. 
Naval  Architecture. 

Third  Edition,  Revised  and  Enlarged,  vii  +  641 
pages.  217  figures.     8vo,  cloth,  $7. 50. 

Thermodynamics  of  the  Steam  Turbine. 

vi  +  282  pages,  103  figures.     8vo,  cloth,  $3.00,  net. 


0& 


'/5 


STEAM-BOILERS. 


CECIL   H.   PEABODY    and    EDWARD   F.   MILLER 

Professor  of  Naval  A  rchitecture  Professor  of  Steam 

and  Marine  Engineering,  '  n-;inecring, 

Massachusetts  Institute  of  Technology. 


SECOXD   EDITION,    REVISED   AXD   EX  L  ARC  ED. 
TOTAL    ISSUE,    TEX   THOUSAND. 


JOHN  S.  PRELL 

Civil  &  Mechanical  Engirt 

SAN  FRANCISCO,  CAU 


NEW    YORK  r 

JOHN    WILEY    &    SONS. 

^ondon  :    CHAPMAN  &  HALL,  Limited. 
1912 


Copyright.  1897,  1908, 

BY 

C  H.  PEABODY  and  E.  F.  MILLER 


THE  SCIENTIFIC   PRESS 

ROBERT    DRUMMONO   AND  COMPANY 

BROOKLYN,    N.    Y. 


Engineering 
Library 


PREFACE   TO    FIRST    EDITION. 


In  this  book  we  have  attempted  to  give  a  clear  and  con- 
cise statement  of  facts  concerning  boilers,  and  of  methods  of 
designing,  making,  managing,  and  caring  for  boilers.  Though 
the  book  is  intended  primarily  for  the  use  of  students  in 
technical  schools  and  colleges,  it  is  hoped  that  it  may  be 
found  useful  to  engineers  in  general. 

There  is  given  a  description  of  various  types  of  boilers  in 
common  use.  Following  this  is  a  discussion  of  combustion, 
corrosion,  and  incrustation,  with  a  statement  of  the  most  recent 
investigations  and  conclusions  on  these  important  subjects. 
We  are  fortunately  able  to  give  a  satisfactory  table  of  the 
compositions  of  American  fuels — the  first,  so  far  as  we  are 
aware,  that  has  been  published. 

A  statement  is  given  of  the  proper  and  of  the  customary 
sizes  and  form  of  furnaces,  and  of  the  methods  of  firing.  In 
the  present  unsatisfactory  condition  of  the  chimney  problem 
we  have  contented  ourselves  with  giving  the  ordinary  theory 
and  pointing  out  its  defects,  together  with  the  common  ways 
of  proportioning  chimneys. 

Tables  of  grate-areas  and  heating-surfaces,  and  of  other 
proportions  of  furnaces  and  boilers,  have  been  made  up  from 
the  Dest  current  practice  for  stationary,  locomotive,  and 
marine   boilers. 

In  the  chapter  on  strength  of  boilers  we  have  given  briefly 
the  methods  and  conditions  for  testing  materials  and  for 
making    boilers,    and    the    properties     which    such    materials 


737412 


Engineering 
Library 


IV  PREFACE. 

should  have.  Especial  attention  is  given  to  the  properties 
and  proportions  of  riveted  joints,  deduced  by  Professors 
Lanza  and  Schwamb  from  tests  at  the  Watertown  Arsenal. 
Simpler  calculations  of  stresses  in  the  members  of  boilers  are 
explained,  and  more  complex  ones,  depending  on  the  theory 
of  elasticity  and  theories  of  beams  and  continuous  girders, 
are  illustrated  by  examples. 

A  description  is  given  of  staying  and  other  details  affect- 
ing the  design  and  construction  of  boilers,  and  of  such  acces- 
sories as  safety-valves,  gauges,  and  steam-traps.  In  order 
to  give  a  conception  of  the  methods  and  conditions  of  boiler- 
making,  we  have  given  a  description  of  a  modern  bciler-shop 
and  the  machinery  and  processes  used  in  it. 

In  the  chapter  on  boiler-testing  we  have  given  the 
methods  used  in  the  laboratories  of  the  Massachusetts  Insti- 
tute of  Technology,  including  gas  analysis,  measurement  of 
air  used,  and  temperature,  determinations  in  the  furnace  and 
chimney. 

Finally,  the  principles  and  methods  set  forth  in  tie  earlier 
chapters  are  brought  together  and  illustrated  by  applying 
them  to  the  design  of  a  boiler  of  a  common  type.  For  our 
own  students  this  chapter  serves  as  an  introduction  to  a 
course  in  machine  design  given  by  Professor  Schwamb,  who 
has  kindly  furnished  us  with  methods  and  materials  which  he 
has  collected  and  developed  in  connection  with  the  design- 
ing of  boilers. 

In  the  appendix  are  given  various  useful  tables,  such  as 
logarithms,  natural  trigonometric  functions,  areas  and  circum- 
ferences of  circles,  proportions  of  rods  and  screws,  and  proper- 
ties of  saturated  steam  C.  H.  P.  and  E.  F.  M. 

Boston,  February  i,  1897. 


PREFACE   TO   SECOND   EDITION. 


A  considerable  amount  of  new  material  and  many  new 
illustrations  have  been  added   in  the   Second   Edition. 

While  but  few  changes  have  been  made  in  the  treatment  of 
the  subject,  each  chapter  has  been  added   to  and  revised. 

A  short  chapter  on  Superheaters  has  been  added;  also  a 
number  of  tables  giving  the  dimensions  of  and  the  floor  space 
occupied  by  the  different  types  of  boilers  and  by  economizers. 

The  subject  of  steam-piping  has  been  treated  at  greater 
length. 

C.  H.  P.  and  E.  F.  M. 

October  i,   1908. 


COXTEXTS. 


CHAPTER  I. 

PACE 

Types  of  Boilers • i 


CHAPTER  II. 
Superheaters 37 

CHAPTER  III. 
Fuels  and  Combustion 47 

CHAPTER  IV. 
Corrosion*  axd  Incrustation 75 

CHAPTER  V. 
Settings,  Furnaces,  and  Chimneys 101 

CHAPTER  VI. 
Power  of  Boilers 143 

CHAPTER  VII. 

Staying  and  Other  Details 1 55 

vii 


viii  CONTENTS. 

CHAPTER  VIII. 

PAGE 

Strength  of  Boilers 1 78 

CHAPTER  IX. 
Boiler  Accessories 252 

CHAPTER  X. 
Shop-practice 304 

CHAPTER  XI. 
Testing  Boilers 333 

CHAPTER  XII. 
Boiler  Design 360 

APPENDIX 395 

INDEX 421 


JOHM  S.  PRELL 

Civil  &  Mechanical  Engineer. 

SAN  FRAN  CISCO,  CAL. 


STEAM-BOILERS. 


CHAPTER    I. 

TYPES   OF    BOILERS. 

Steam-BOILERS  may  be  classified  according  to  l.helr  form 
and  construction  or  according  to  their  use.  Thus  we  have 
horizontal  and  vertical  boilers,  internally  and  externally  fired 
boilers,  shell-boilers  and  sectional  boilers,  fire-tube  and  water- 
tube  boilers:  the  several  features  mentioned  may  be  combined 
in  various  ways  so  as  to  give  rise  to  a  large  number  of  kinds 
and  forms  of  boilers.  Again,  we  have  stationary,  locomotive, 
and  marine  boilers,  together  with  a  variety  of  portable  and 
semi-portable  boilers.  Locomotive  boilers  are  always  shell- 
boilers,  internally  fired,  and  with  fire-tubes;  and  the  re- 
strictions of  the  service  have  developed  a  form  that  has 
changed  little  from  the  beginning,  except  in  the  direction  of 
increased  size  and  power.  Marine  boilers  present  a  much 
larger  variety  of  form  and  construction,  depending  on  the 
steam-pressure  used  and  the  size  and  service  of  the  vessel  to 
which  they  are  supplied.  The  Scotch  or  drum  boiler  is  more 
widely  used  than  any  other  form  at  present,  but  the  tendency 
to  use  high-pressure  steam  has  led  to  the  introduction  of  vari- 
ous forms  of  water-tube  boilers  for  marine  work.  The  variety 
of  forms  and  methods  of  construction  of  stationary  boilers  is 
very  wide:  each  country  and  section  of  a  country  is  likely  to 
have   its  own  favorite  type.      Thus  in   New  England,  where 


2  STEAM-BOILERS. 

the  water  is  good,  cylindrical  tubular  boilers  are  largely  used; 
in  some  of  the  Western  States,  where  water  contains  mineral 
impurities,  flue-boilers  are  preferred ;  and  in  England,  the 
Lancashire  and  Galloway  boilers  are  favored;  and  again, 
various  forms  of  sectional  and  water-tube  boilers  are  now 
widely  used. 

Cylindrical  Tubular  Boiler. — This  type  of  boiler  is  shown 
by  Figs,  i  and  2  and  by  Plate  I.  It  consists  essentially  of  a  cylin- 
drical shell  closed  at  the  ends  by  two  flat  tube-plates,  and  of 
numerous  fire-tubes,  commonly  having  a  diameter  of  three  or 
four  inches.  About  two  thirds  of  the  volume  of  the  boiler  is 
filled  with  water,  the  other  third  being  reserved  for  steam. 
The  water-line  is  six  or  eight  inches  above  the  top  row  of 
tubes.  The  tube-plates  below  the  water-line  are  sufficiently 
stayed  by  the  tubes ;  above  the  water-line  the  flat  plates  are 
stayed  by  through  rods  or  stays  as  in  Plate  I,  by  diagonal 
stays  like  those  shown  by  Fig.  63,  page  159,  or  otherwise.  A 
pair  of  cylindrical  boilers  in  brick  setting  are  shown  by  Figs. 
39  and  40,  on  pages  102  and  103,  with  the  furnaces  under 
the  front  (right-hand  1  end.  The  products  of  combustion  pass 
back  over  a  bridge-wall,  limiting  the  furnace,  to  the  back  end, 
then  forward  through  the  tubes  and  up  the  uptake  to  the  flue 
which  leads  to  the  chimney. 

The  shell  commonly  extends  beyond  the  front  tube-plate, 
as  shown  at  the  right  in  Fig.  1,  and  is  cut  away  to  facilitate 
the  arrangement  of  the  uptake.  The  boiler  is  usually  sup- 
ported by  cast-iron  brackets  riveted  to  the  shell ;  the  front 
brackets  may  rest  on  or  be  fixed  to  the  supporting  side  walls, 
but  the  rear  brackets  should  be  given  some  freedom  to  avoid 
unduly  straining  the  boiler  by  expansion.  Thus  the  rear 
brackets  may  rest  on  rollers,  which  in  turn  bear  on  a  horizontal 
iron  plate.  The  expansion  takes  place  toward  the  back  end  of 
the  boiler,  and  to  allow  for  this  expansion  a  space  is  left 
between  the  back  tube-sheet,  and  the  arch  of  fire-brick  back 
of  the  boiler. 


TYPES    OF  BOILERS. 


STEAM-BOILERS. 


TYPES  OF  BOILERS.  - 

The  boilers  shown  by  Figs,  i  and  2  and  by  Plate  I  each  have 
two  steam-nozzles,  one  near  each  end.  The  safety-valve  is 
usually  attached  to  the  front  nozzle,  which  is  above  the  fur- 
nace. The  steam-pipe  leading  steam  from  the  boiler  is  at- 
tached to  the  rear  nozzle,  which  is  over  the  back'  end  of  the 
boiler,  where  ebullition  is  less  violent,  and  consequently  there 
is  less  danger  that  water  will  be  thrown  into  the  steam-pipe. 

Boilers  of  this  type  commonly  have  a  manhole  on  top  :itcu 
the  middle,  and  a  hand-hole  near  the  bottom  of  2ach  tcbe- 
sheet,  as  shown  on  Plate  I,  to  give  access  to  ths  interior  of 
the  boiler  and  to  facilitate  washing  out.  Mai'],  boilers  are 
now  made  with  a  manhole  near  the  bottom  of  the  front  tube- 
sheet,  in  addition  to  the  one  on  top.  All  parts  of  the  boiler 
can  then  be  cleaned  and  inspected  whenever  desirable.  Some 
of  the  lower  tubes  must  be  left  out  when  there  is  a  manhole 
in  the  tube-sheet,  but  this  is  of  small  consequence,  as  the 
lower  tubes  are  not  efficient,  and  enough  heating-surface  can 
be  provided  elsewhere.  The  omission  of  the  lower  tubes  re- 
quires also  special  stays  for  the  portion  of  the  tube-sheet  left 
unsupported. 

The  fecd-pipe  for  the  boiler  shown  by  Plate  I  enters  the 
front  head  at  the  left,  below  the  water-line,  and  runs  toward 
the  back  end  of  the  boiler,  where  it  may  end  in  a  perforated 
pipe  leading  across  the  boiler.  The  feed-pipe  may  enter  the 
top  of  the  boiler,  near  the  back  end,  and  terminate  in  a  similar 
perforated  transverse  pipe  below  the  water-line. 

A  bhnc-off pipe  leads  from  the  bottom  of  the  shell  near  the 
back  tube-sheet.  On  the  blow-off  pipe  there  is  a  plug  or  valve 
which  may  be  opened  when  steam  is  up,  to  blow  out  mud  and 
soft  scale  that  may  collect  in  the  boiler.  The  boiler  is  com- 
monly set  with  a  slight  inclination  toward  the  rear  so  that 
mud  may  collect  near  the  blow-off  pipe.  The  boiler  may  be 
emptied  by  allowing  the  water  to  run  out  at  the  blow-off  pipe. 

About  half  of  the  shell,  two  thirds  of  the  back  tube-sheet, 
and  all  the   inside  surface  of  the  tubes  come    in    contact  with 


STEAM-BOILERS. 


the  products  of  combustion  and  form  the  heating-surface ;  all 
the  heating-surface  is  below  the  water-line. 

The  boiler-setting,  shown  by  Figs.  39  and  40  on  pages 
102  and  103  is  made  of  brick  laid  in  cement  or  mortar;  all 
parts  that  are  directly  exposed  to  the  fire  are  lined  with  fire- 
brick. The  walls  have  confined  air-spaces  to  reduce  transmis- 
sion of  heat.  The  boiler  front  is  commonly  made  of  cast  iron, 
and  has  fire-doors  leading  to  the  furnace,  and  ash-pit  doors 
opening  from  the  ash-pit,  or  space  below  the  grate ;  there  are 
also  large  doors  giving  access  to  the  tubes  through  the 
smoke-box  at  the  front  end  of  the  boiler.  The  furnace  is 
formed  by  the  side  walls,  the  bridge,  and  the  lower  part  of  the 
boiler  front,  which  latter  is  lined  with  fire-brick  above  the 
grate.  Doors  through  the  rear  wall  give  access  to  the  space 
back  of  the  bridge.  The  top  of  the  boiler  is  covered  by  a 
brick  arch  or  by  non-conducting  material. 

Two-flue  Boiler. — The  cylindrical  flue-boiler  differs  from 
the  tubular  boiler  mainly  in  replacing  the  fire-tubes  by  one 
or  more  large  flues.      Fig.  3   shows  such  a  boiler  with  two 


Fig.  3. 


flues.      This  type  of  boiler  is  usually  longer   than  a  tubular 
boiler,    but    even   so    it    has    less    heating-surface  and   is  less 
efficient    in   the  use  of  coal.      Nevertheless  the  greater  sim- 
plicity and  accessibility  for  cleaning  recommend  it  where  feed 
water  is  bad. 

The  setting  of  a  flue-boiler  resembles  that   for  the  cylin- 


TYPES  OF  BOILERS. 


drical 


tubular-boiler.      The  figure  shows  two  loops  at  the  top 

of  the  shell  for  hanging  the 
boiler;  a  crude  method  of  sup- 
porting, suitable  only  for  small 
and  short  boilers. 

Plain  Cylindrical  Boiler. — 
In  places  where  fuel  is  very 
cheap,  especially  where  it  is  a 
waste  product,  as  at  sawmills, 
the  plain  cylindrical  boiler  is  fre- 
quently used.  Its  external  ap- 
pearance is  similar  to  that  of  the 
two-flue  boiler  (Fig.  3),  except 
that  there  are  no  flues  and  the 
ends  are  commonly  hemispheri- 
cal or  else  curved  to  a  radius 
equal  to  the  diameter  of  the 
*  shell.  Such  plain  cylindrical 
~  boilers  are  also  employed  to  util- 
ize the  waste  gases  from  blast- 
furnaces. They  are  commonly 
30  to  42  inches  in  diameter  and 
from  20  to  40  feet  long.  They 
have  been  made  70  feet  long. 
With  such  extreme  lengths  spe- 
cial care  must  be  taken  to  insure 
equal  distribution  of  the  weight 
to  the  supports  and  to  provide 
for  expansion. 

Lancashire  Boiler.  —  This 
boiler,  shown  by  Fig.  4,  is  a  two- 
flue  shell-boiler  with  furnaces 
in  the  tubes;  it  is  therefore  an 
internally-fired  boiler,  in  which 
it     differs    from    the     two     pre- 


8  STEAM-BOILERS. 

ceding  types,  which  are  externally-fired.  The  chief  difficulty 
in  the  design  of  these  boilers  is  to  provide  sufficiently  large 
furnaces  without  making  the  external  shell  too  large.  As  com- 
pared with  the  cylindrical  tubular  boiler,  this  boiler  will  be 
sure  to  have  long,  narrow  grates,  with  a  shallow  ash-pit  and  a 
low  furnace-crown :  the  boiler  also  appears  to  be  deficient  in 
heating-surface.  In  compensation,  radiation  and  loss  of  heat 
from  the  furnace  are  almost  entirely  done  away  with,  and  the 
thick  outside  shell,  with  its  riveted  joints,  is  not  exposed  to 
the  fire,  as  with  the  tubular  boiler.  The  flues  are  made  in 
short  sections  riveted  together  at  the  ends,  thus  forming  a 
series  of  stiffening  rings  that  add  very  much  to  the  strength 
of  the  flues  against  collapsing.  Conical  through-tubes,  ver- 
tical or  inclined,  give  increased  heating-surface,  break  up  the 
currents  of  the  hot  gases,  improve  the  circulation  of  the  water, 
and  strengthen  the  flues.  These  tubes  are  small  enough  at 
the  lower  end  to  pass  through  the  hole  cut  in  the  flue  for  the 
upper  end,  and  thus  are  readily  put  in  or  taken  out  for  repairs. 

The  flat  plates  at  the  ends  of  the  shell  are  stayed  by 
gusset-stays  or  triangular  flat  plates  to  the  shell  of  the  boiler. 
The  boiler  is  provided  with  a  manhole  near  the  back  end  and 
a  safety-valve  near  the  front  end.  Steam  is  taken  through  a 
horizontal  dry-pipe,  perforated  on  the  top. 

Galloway  Boiler. — This  boiler  has  two  furnace-flues  at  the 
front  end,  like  the  Lancashire  boiler.  Beyond  the  furnace 
the  two  flues  merge  into  one  broad  flue,  having  the  upper  and 
lower  surfaces  stayed  by  numerous  conical  through-tubes,  like 
those  shown  in  Fig.  4  for  the  Lancashire  boiler. 

Cornish  Boiler. — This  boiler  was  developed  in  conjunction 
with  the  Cornish  engine,  and  both  boiler  and  engine  long  had 
a  reputation  for  high  efficiency.  It  differed  from  the  Lanca- 
shire boiler  in  that  it  had  but  one  flue;  it  formerly  did  not 
have  cross-tubes.  The  one  furnace  of  the  Cornish  boiler,  with 
a  given  diameter  of  shell,  can  have  better  proportions  than 
the  two  furnaces  of  the  Lancashire  boiler,  but  there  is  even 


TYPES  OF  BOILERS.  g 

greater  difficulty  to  get  sufficient  grate-area  and  heating-sur- 
face- The  high  economy  shown  by  these  boilers  when  used 
with  the  Cornish  pumping-engine  was  due  to  a  slow  rate  of 
combustion,  and  to  the  skill  and  care  of  the  attendant,  who 
was  usually  both  engineer  and  fireman,  and  who  was  stimu- 
lated by  a  system  of  competition  and  awards,  maintained  by 
the  mine-owners  in  that  district. 

The  Lancashire  and  the  Cornish  boilers  are  set  in  brickwork 
which  forms  flues  leading  around  the  outside  shell,  thus  mak- 
ing the  shell  act  as  heating-surface.      Fig.  5  gives  a  cross-sec- 


Fig.  5. 


tion  of  the  Lancashire  boiler  and  its  setting.  After  the  gases 
from  the  fires  leave  the  internal  flues  they  are  directed  into 
the  flue  a  and  come  forward ;  then  they  are  transferred  to  the 
flue  b  and  pass  backward  ;  finally  they  come  forward  in  the 
flue  c,  and  are  then  allowed  to  pass  to  the  chimney.  This 
forms  what  is  known  as  a  wheel-draught.  In  some  cases  the 
gases  divide  at  the  rear  and  come  forward  through  both  side 


IO  STEAM-BOILERS. 

flues  a  and  b,  and  uniting  pass  back  through  c  and  thence  to 
the  chimney,  forming  a  split-draught. 

Vertical  Boilers. — Boilers  of  this  type  have  a  cylindrical 
shell  with  a  fire-box  in  the  lower  end,  and  with  fire-tubes  run- 
ning from  the  furnace  to  the  top  of  the  boiler.  Large  verti- 
cal boilers  have  a  masonry  foundation  and  a  brick  ash-pit ; 
small  vertical  boilers  have  a  cast-iron  ash-pit  that  serves  as 
foundation.  Vertical  boilers  require  little  floor-space;  if 
properly  designed  they  give  good  economy,  or  they  may  be 
made  light  and  powerful  for  their  size,  when  economy  is  not 
important. 

Fig.  6  shows  a  large  vertical  boiler  designed  by  Mr. 
Manning.  It  is  made  20  to  30  feet  high,  so  that  there  is  a 
large  heating-surface  in  the  tubes.  The  shell  is  enlarged  at 
the  fire-box  to  provide  a  larger  furnace  and  more  area  on  the 
grate.  The  internal  shell  which  forms  the  fire-box  is  joined 
to  the  external  shell  by  a  welded  iron  ring  called  the  founda- 
tion-ring. This  internal  shell  should  be  made  of  moderate 
thickness  to  avoid  burning  or  wasting  away  under  the  action 
of  the  fire.  Being  under  external  pressure,  the  shell  of  the 
fire-box  must  be  stayed  to  avoid  collapsing.  For  this  pur- 
pose it  is  tied  to  the  outside  shell  at  intervals  of  four  or  five 
inches  each  way,  by  bolts  that  are  screwed  through  both 
shells  and  riveted  over  cold,  on  both  ends.  The  stays  near 
the  bottom  have  each  a  hole  drilled  from  the  outside  nearly 
through  to  the  inside  end.  Should  any  stay  break  or  become 
cracked,  steam  will  escape  and  give  warning  to  the  fireman. 

The  tubes  are  arranged  in  concentric  circles,  leaving  a 
space  about  ten  inches  in  diameter  at  the  middle  of  the 
crown-sheet;  the  corresponding  space  in  the  upper  tube- 
sheet  provides  for  the  attachment  of  the  nozzle  for  the  steam 
outlet. 

There  are  numerous  hand-holes  in  the  shell  outside  of  the 
fire-box,  some  near  the  crown-sheet,  and  some  near  tne  foun- 
dation-ring,  and  these  are  the  only  provision  for  cleaning  the 


TYPES  OF  BOILERS. 


31 


FEED  PIPE 


WATER  LEVEL 


WiWJUL±2^=r 


\^W9B»\ 


Fig.  6. 


12 


STEAM-BOILERS. 


boiler,  which  consequently  is  adapted  for  the  use  of  good 
feed-water  only.  The  feed-pipe  enters  the  shell  at  one  side 
and  extends  across  the  boiler;  it  is  perforated  to  distribute 
the  feed-water. 

The  sides   of  the   fire-box,  the   remaining  surface   of   the 
tube-sheet  allowing  for  the  holes  for  the  tubes,  and  the  inside 


Fig.  7. 

of  the  tubes  up  to  the  water-line  form  the  heating-surface; 
the  inside  of  the  tubes  above  the  water-line  form  the  super 


TYPES  OF  BOILERS. 


13 


healing-surface,  since  it  transmits  heat  from  the  gases  to  the 
steam  and  superheats  it. 

This  type  ol  boiler  has  found  favor  at  factories  where 
floor-space  is  valuable,  since  a  powerful  battery  of  boilers  may 
be  placed  in  a  small  fire-room. 

A  small  vertical  boiler  adapted  for  hoisting,  pile-driving, 
and  other  light  work  is  shown  by  Fig.  7.  It  commonly  has 
a  short  smoke-pipe,  into  which  the  exhaust  steam  from  the 
engine  is  turned  to  form  a  forced  draught  and  give  rapid 
combustion.  Under  this  treatment  the  upper  ends  of  the 
tubes  frequently  give  trouble  by  leaking.  To  avoid  this  diffi- 
culty the  tubes  are  sometimes  ended  in  a  sunken  or  submerged 
tube-sheet  which  is  kept  below  the  water-line,  as  shown  by 
Fig.   8.       The    space    between   the    edge    of    the    tube-sheet 


Fig.  8. 

and  the  outside  shell  is  likely  to  be  contracted,  and  not  to 
give  proper  exit  for  the  steam  formed  on  the  tubes  and 
crown-sheet.  Furthermore,  the  cone  forming  the  smoke- 
chamber  above  the  tube-sheet  is  subjected  to  external  pres- 
sure and  is  likely  to  be  weak. 

A  form  of  vertical  boiler  having  a  sunken  tube-plate  is 
shown  by  Fig.  9.  It  was  at  one  time  much  used  for  steam 
fire-engines,  but  to  save  weight  it  was  so  crowded  with  tubes 


14 


STEAM-BOILERS. 


and   the  water-spaces  were   so  contracted  that   it   gave  much 
trouble  when  forced,  as  at  a  fire. 

Fire-engine  Boiler. — A    boiler    for   a    steam    fire-engine 
should  be  light  and  compact,  able  to  make  steam  quickly  and 


Fig.  9. 

to  steam  freely  when  urged.  They  have  small  water-space 
and  large  heating-surface  for  their  size,  but  are  not  economi- 
cal in  the  use  of  fuel.  It  is  customary  to  use  cannel-coal  for 
fire-engines,  as   it  burns   freely  without    clogging.      A  forced 


TYPES  OF  BOILERS.  1 5 

draught  is  obtained  by  exhausting  steam  up  the  smoke-pipe. 
When  standing  in  the  engine-house  ready  for  duty  the 
boilers  are  kept  hot  by  connecting  them  to  a  heating- 
boiler  in  the  basement.  The  connection  is  so  made  with 
snap-valves  that  it  is  broken  by  pulling  the  fire-engine  out  of 
position. 


Fig.  10. 


Scotch  Boilers. — A  single-ended  three-furnace  Scotch 
marine  boiler  is  shown  in  perspective  by  Fig.  10;  Fie;,  tt 
gives  the  working  drawings  of  a  similar  boiler  with  two  fur- 
naces. The  arrangement  of  the  furnaces  in  the  flues,  is  simi- 
lar to  that  for  the  Lancashire  boiler,  shown,  by  Fig.  4.  The 
furnace-flue    leads    into   a    combustion-chamber,  from    which 


1 6  STEAM-BOILERS. 

the  products   of   combustion  pass   through    fire-tubes  to  the 
uptake,  which  is  bolted  onto  the  front  end  of  the  boiler. 

The  flues  are  from  three  and  a  half  to  four  and  a  half 
feet  in  diameter;  the  size  of  the  boiler  depends  on  the 
number  and  size  of  the  flues.  Large  boilers  have  as  many 
as  four  flues.  A  three-furnace  boiler  commonly  has  three 
combustion-chambers,  while  a  four-furnace  boiler  may  have 
two,  into  each  one  of  which  two  furnaces*  lead.  Double- 
ended  boilers  have  furnaces  at  each  end,  and  resemble 
two  single-ended  boilers  placed  back  to  back.  A  double- 
ended  boiler  is  lighter,  cheaper,  and  occupies  less  space  than 
two  single-ended  boilers.  In  the  best  practice  there  are 
two  distinct  sets  of  combustion-chambers  for  the  two  sets 
of  furnaces.  To  still  further  lighten  double-ended  boilers, 
common  combustion-chambers  for  corresponding  furnaces  at 
the  two  ends  have  been  used.  The  results  from  such 
boilers  have  not  been  satisfactory,  more  especially  when 
used  under  forced  draught  in  the  closed  stoke-holes  of  war- 
ships;  there  has  been  so  much  trouble  from  leaky  tubes 
under  such  conditions  that  forced  draught  has  been  aban- 
doned in  many  cases,  and  ships  have  consequently  failed  to 
make  the  speed  anticipated. 

The  circulation  of  water  is  defective  in  all  Scotch  boilers, 
and  more  especially  in  double-ended  boilers.  Considerable 
time — three  or  four  hours — is  always  allowed  for  raising  steam. 
Frequently  some  arrangement  is  made  for  drawing  cold  water 
from  the  bottom  of  the  boiler  and  returning  it  near  the  water- 
line,  while  steam  is  raised.  Haste  and  lack  of  care  are  liable 
to  cause  leakage  from  unequal  expansion.  The  flue  has  the 
highest  temperature  of  any  part  of  the  boiler  and  consequently 
expands  the  most,  so  that  some  allowance  for  expansion  must 
be  made  or  it  will  strain  the  tube-sheets  and  cause  leaks.  The 
methods  of  providing  for  expansion  and  at  the  same  time 
stiffening  the  flues  against  collapsing  under  external  pressure 
are  shown  on  pages  221  to  236,  and  will  be  described  in  de- 
tail later  on. 


TYPES    OF  BOILERS. 


•7 


1 8  STEAM-BOILERS. 

Locomotive-boilers. — The  typical  American  locomotive- 
boiler  is  shown  by  Plate  II.  Fig.  12  gives  a  perspective  view 
of  a  boiler  of  the  locomotive  type  used  for  small  factories,  or 
where  steam  is  required  temporarily ;  it  has  no  permanent 
foundation,  but  is  supported  on  brackets  at  the  fire-box  and 
by  a  pedestal-bearing  on  rollers  near  the  back  end. 

The  locomotive-boiler  consists  essentially  of  a  rectangular 
fire-box  and  a  cylindrical  barrel  through  which  numerous  tubes 
pass  from  the  fire-box  to  the  smoke-box,  which  forms  a  con- 
tinuation of  the  barrel,  and  from  which  the  products  of  com- 
bustion pass  up  the  smoke-stack. 

The  fire-box  is  joined  to  the  outer  shell  at  the  bottom  by 
a  forged  rectangular  foundation-ring,  similar  (except  in  shape) 


Fig. 


to  the  foundation-ring  of  a  vertical  boiler.  Near  this  ring  are 
several  hand-holes  for  clearing  out  the  space  between  the  fire- 
box and  the  shell,  commonly  called  the  water-leg.    The  boiler 


TYPES    OF    BOILERS. 


19 


also  has  a  manhole  at  the  top  of  the  barrel.  The  water-leg  is 
Stayed  by  screwed  stay-bolts  riveted  cold  at  the  end-,. 

The  flat  crown-sheet  is  stayed  to  a  system  of  crown-bars 
which  rest  on  the  side  sheets  of  the  fire-box  and  are  also  slung 
from  the  shell. 

Plate  III  shows  a  locomotive-boiler  with  a  flattened  top  over 
the  fire-box  to  which  the  crown-sheet  is  stayed  by  through-bolts. 

The  excessive  compression  brought  to  the  sheets,  forming 
the  inner  sides  of  the  water-leg,  by  the  crown-bars  which  get 
an  end  support  at  these  sheets  and  the  great  depth  required  in  the 
crown-bar  in  order  to  give  the  strength  needed,  have  made  it 
impracticable  to  use  crown-bars  on  boilers  carrying  more  than 
200  lbs.  of  steam-pressure. 

The  method  shown  by  Plate  III  is  commonly  adopted  on 
large  boilers  of  this  class.  The  stay-bolt  has  a  tapering  head 
which  is  drawn  into  a  tapering  hole  in  the  crown-sheet.  This 
makes  a  tight  joint  and  does  not  increase  to  any  extent  the  amount 
of  metal  in  contact  with  the  crown-sheet. 

The  whole  matter  of  staying  will  be  discussed  more  fullv  in 
the  chapter  on  staying. 

The  tubes  for  a  locomotive-boiler  are  smaller  than  for  a  sta- 
tionary boiler  and  are  spaced  much  more  closely.  Generally 
about  2-inch  tubes  are  used  in  locomotives,  although  in  some 
cases  smaller  tubes  have  been  used.  The  tubes  are  spaced  at 
the  intersection  of  sets  of  parallel  lines  drawn  at  angles  of  300  and 
1500  with  reference  to  a  horizontal  line. 

By  this  means  a  greater  number  of  tubes  can  be  gotten  into 
a  given  space  than  could  be  done  by  spacing  in  vertical  and 
horizontal  rows,  as  is  customary  in  horizontal  multitubular  boilers 
like  Figs.  1  and  2  and  Plate  I.  This  is  to  obtain  a  large  heating- 
surface  required  by  the  high  rate  of  combustion,  which  often 
exceeds  one  hundred  pounds  of  coal  per  square  foot  of  grate- 
surface  per  hour.  The  boiler  works  under  a  strong  forced 
draught,  produced  by  throwing  the  exhaust  up  the  smoke-stack. 

The  boiler  is  fastened   rigidly   to   the  frame  of  the  locomo- 


20  STEAM-BQILERS. 

m 

tive  at  the  smoke-box  end;  a  small  longitudinal  motion  on  the 
frame  at  the  fire-box  end  is  provided  by  expansion- pads,  shown 
by  Fig.  4,  Plate  II. 

Locomotive  Type  of  Boiler. — Reference  has  already  been 
made  in  connection  with  Fig.  12  to  a  boiler  of  locomotive  type 
used  for  stationary  purposes.  Plate  IV  shows  a  modification 
of  the  locomotive  type  designed  by  Mr.  E.  D.  Leavitt  to  give- 
high  evaporative  efficiency.  The  boiler  represented  has  a  barrel 
90  inches  in  diameter,  and  it  is  34  feet  4  inches  long  over  all. 
The  working  pressure  is  185  pounds. 

The  fire-box  of  this  boiler  is  spread  at  the  bottom  to  give 
increased  grate-area,  and  contains  two  separate  furnaces,  shown 
by  the  section  A  A  on  Plate  IV.  The  products  of  combus- 
tion pass  through  openings,  shown  by  section  BB,  into  a  com- 
bustion-chamber, which  has  the  section  shown  at  CC.  From 
the  combustion-chamber,  the  gases  pass  through  tubes  to  the 
smoke-box  and  uptake.  As  far  as  the  combustion-chamber 
the  top  of  the  boiler  is  flattened  to  facilitate  the  staying  of  the 
crown-sheets  of  the  furnace,  passages,  and  combustion-cham- 
ber; the  barrel  of  the  boiler  beyond  the  combustion-chamber 
is  cylindrical. 

The  boiler  is  somewhat  complicated  in  construction  and 
staying,  and  must  be  handled  with  care,  especially  in  starting,, 
to  avoid  straining  from  unequal  expansion.*  It  is  adapted  for 
the  use  of  good  feed-water  only. 

Boilers  of  the  locomotive  type  were  at  one  time  used  for 
torpedo-boats.  The  fire-box  was  made  shallower  than  for 
locomotive-boilers,  and  forced  draught  in  a  closed  stoke-hole 
was  used,  the  rate  of  combustion  being  even  higher  than  on 
locomotives.  Whatever  may  have  been  the  reasons,  it  was  a 
fact  that  this  type  of  boiler,  which  is  very  reliable  on  locomo- 
tives, gave  much  trouble  in  torpedo-boats. 

Water-Tube  Boilers. — The  boilers  thus  far  considered 
have  an  external  shell  containing  a  large  body  of  water.  Heat 
is  communicated   to  the  water  through  the  shells  or  through 


TYPES  OF  BOILERS.  21 

the  sides  of  internal  furnaces,  and  also  by  carrying  the  gases 
through  tubes  or  flues.  The  boilers  and  water  contained,  are 
heavy  and  cumbersome,  and  the  shells  under  high  pressure 
must  be  made  very  thick.  If  the  boiler  fails  either  through 
some  defect  or  through  carelessness  of  attendants,  a  disastrous 
explosion  is  likely  to  take  place.  If  properly  designed  and 
made  and  if  cared  for  by  competent  and  careful  attendants 
they  are  safe,  reliable,  and  durable.  The  large  mass  of  hot 
water  tends  to  keep  a  steady  pressure,  though  at  the  expense 
of  rapidity  of  raising  steam  or  of  meeting  a  sudden  demand 
for  more  steam. 

A  large  number  of  water-tube  boilers  of  all  sorts  of  shapes 
and  methods  of  construction  has  been  devised  to  overcome 
the  admitted  defects  of  shell-boilers.  They  all  have  the 
larger  part  of  their  heating-surface  made  up  of  tubes  of  moder- 
ate size  filled  with  water.  They  all  have  some  form  of  separa- 
tors, drum,  or  reservoir  in  which  the  steam  is  separated  from 
the  water;  some  of  these  boilers  have  a  shell  of  consider- 
able size,  thus  securing  a  store  of  hot  water  and  a  good  free- 
water  surface  for  disengagement  of  steam.  Such  shell,  drum, 
or  reservoir  is  either  kept  away  from  the  fire  or  is  reached 
only  by  gases  that  have  already  passed  over  the  surface  of 
water-tubes. 

The  tubes  are  of  moderate  or  small  diameter,  and  so  can 
be  abundantly  strong  even  when  made  of  thin  metal.  Even 
if  a  tube  fails  through  defect  in  manufacture  or  through  wast- 
ing during  service,  it  will  not  cause  a  true  explosion ;  and  yet 
the  failure  of  a  tube  in  a  confined  boiler  or  fire-room  has  fre- 
quently caused  death  by  scalding. 

Water-tube  boilers  may  be  made  light,  powerful,  and 
compact,  and  are  well  adapted  for  use  with  forced  draught. 
Steam  may  be  raised  rapidly  from  cold  water,  but  pressure 
falls  as  rapidly  if  the  fire  loses  intensity,  and  fluctuations  in 
pressure  are  likely  to  occur.  The  two  greatest  difficulties  are 
to  secure  a  proper    circulation    of  water    through    the    tubes 


2  2  Si  EA  M -BOILERS. 

and  to  properly  separate  the  steam  from  the  water.  There- 
are  many  joints  that  may  give  trouble  by  leaking,  and  some 
types  have  numerous  hand-holes  for  cleaning  the  tubes,  which 
may  further  increase  the  chances  of  petty  leaks. 

A  few  water-tube  boilers  will  be  described  as  illustrations ; 
many  others  equally  good  will  be  passed  by,  since  it  will  be 
impossible  to  describe  all. 

Babcock  and  Wilcox  Boiler.— This  boiler,  which  is 
shown  by  Figs.  13  and  14,  is  a  water-tube  boiler  having  one  or 
two  cylindrical  drums  at  the  top  from  either  end  of  which  are 
suspended  '"headers"  into  which  the  tubes  running  from  end 
to  end  are  expanded. 

The  headers  are  made  of  steel  castings  or  forgings,  box-like 
in  shape,  with  holes  for  tubes  staggered  so  thaf  the  tubes  taken 
as  a  whole  are  in  horizontal  rows,  but  not  in  vertical  rows — an 
arrangement  that  gives  a  better  spreading  of  the  products  of 
combustion  among  the  tubes. 

Opposite  the  end  of  each  tube  there  is  a  hand-hole,  as  shown. 
Each  header  is  connected  with  the  corresponding  header  at  the 
opposite  end  by  the  tubes  making  a  "section."  The  capacity  of 
a  boiler  of  this  class  is  increased  by  increasing  the  number  of 
tubes  in  a  section  and  by  increasing  the  number  of  sections  con- 
nected to  the  drum  or  drums  at  the  top:  thus  a  boiler  12  wide 
and  9  high  would  have  12  sections  and  9  tubes  in  each  header. 
If  there  were  a  very  strong  draught  it  might  be  advisable  to  have 
more  tubes  in  a  header. 

A  double-deck  boiler  is  one  where  a  second  header  is  joined 
to  the  end  of  the  first  header.  The  two  headers  are  joined  by 
a  piece  of  tube  which  is  expanded  into  each.  Two  headers, 
each  9  high,  when  joined  in  this  way  make  18  high. 

By  means  of  a  special  tile  made  to  fit  between  the  tubes  the 
gases  are  obliged  to  circulate,  as  shown  by  the  arrows. 

The  gases  escape  out  of  the  back  wall.  In  some  cases  where 
there  is  not  much  room  the  gases  have  been  brought  up  between 
the  drums  at  the  back  end,  thus  enabling  the  back  wall  to  be 


TYPES    OF    BOILERS. 


23 


24 


STEAM-BOILERS. 


against  the  wall  of  the  building.  The  lower  half  of  the  cylin- 
drical shell  serves  as  heating-surface,  but  it  is  at  such  a  height 
above  the  fire  and  is  so  shielded  by  the  water-tubes  that  it  is  not 
liable  to  be  overheated.  The  boiler  is  hung  from  cross-girders 
front  and  back,  which  in  turn  are  supported  on  iron  columns, 
and  the  brick  setting  is  only  a  screen  to  retain  the  heat. 

The  circulation  of  the  water  in  the  boiler  is  down  from  the 
shell  at  the  rear  to  the  water-tubes,  forward  and  upward  through 
the  tubes,  in  which  course  it  is  partially  vaporized  and  conse- 
quently has  a  less  average  density,  then  up  into  the  shell  at 
the  front,  where  the  steam  and  water  separate;  the  water  in  the 
shell  flows  continually  from  the  front  to  the  rear  to  supply  the 
current  through  the  tubes. 

Beneath  the  back  headers  there  is  a  mud-drum  into  which 
scale  settles.  The  blow-off  pipe  leads  from  this  mud-drum  out 
through  the  setting. 

Heine  Boiler. — This  boiler,  shown  by  Fig.  15,  consists  of 
one  or  two  drums,  depending  on  the  size  of  the  boiler,  with  a  rec- 
tangular box-like  water-leg  connected  at  each  end. 

These  legs  are  built  out  of  plate  and  riveted  to  the  drum  or 
drums. 

Tubes  run  from  leg  to  leg.  Opposite  the  end  of  each  tube 
there  is  a  hand-hole  through  which  the  tube  may  be  expanded 
or  cleaned  from  scale.  The  boiler  is  set  with  the  back  end  con* 
siderably  lower  than  the  front  end,  as  shown  by  the  cut. 

The  gases  are  made  to  circulate,  as  indicated  by  the  arrows. 

The  feed-water  is  taken  into  a  small  drum  inside  the  main 
drum.  It  becomes  heated  here  and  deposits  some  of  the  lime 
salts,  which  are  generally  found  in  feed-water.  These  deposits 
are  blown  out  from  time  to  time  through  the  pipe  shown.  A 
similar  blow-off  connection  is  shown  at  the  bottom  of  the  back 
water-leg. 

The  water  circulation  is  from  the  front  towards  the  back  in 
the  drum  and  from  the  back  towards  the  front  in  the  tubes. 

A  mixture  of  steam  and  water  rushes  out  of  the  tubes  at  the 


TYPES    OF    BOILERS. 


25 


front  end  and  uj>  into  the  drum  where  it  strikes  against  a  deflect- 
ing plate  placed  so  as  to  keep  water  from  being  sprayed  into  the 
steam  space. 

A  similar- plate  is  to  be  found  in  the  drum  of  the  Babcock 
and  Wilcox  boiler.  The  velocity  into  the  drum  is  greater  in  the 
Babcock  and  Wilcox  than  in  the  Heine. 

The  water-legs  of  the  Heine  boiler  are  stayed  by  hollow  stays 


Fig.  15. 

expanded  or  screwed  into  the  two  plates  at  points  located  between 
the  tubes. 

The  Stirling  Boiler. — This  boiler,  shown  by  Fig.  16,  has 
three  cylindrical  drums  at  the  top  and  a  larger  drum  at  the 
bottom,  connected  by  tubes  having  a  slight  curvature  at  the 
ends.  The  two  forward  drums  at  the  top  have  also  a  connec- 
tion below  the  water-line  through  pipes  not  indicated.  All 
three  upper  drums  have  their  steam-spaces  connected  by 
piping.      The  water-line  is  indicated  by  a  dotted  line. 


26 


STEAM-BOILERS. 


The  feed- water  is  introduced  into  the  rear  upper  drum, 
from  which  it  passes  down  through  the  rear  system  of  pipes, 
which  act  mainly  as  a  feed-water  heater,  and  enter  the  lower 
drum,  where  the  water  deposits  any  lime  compound  that  it 
may  contain,  from  whence  it  may  be  blown  out  at  intervals. 
Fire-brick  bridges  cause  the  products  of  combustion  to  pass 
in  succession  through  the  three  systems  of  water-tubes  as 
shown  by  the  arrows. 


Fig.  i 6. 


The  circulation  through  the  tubes  is  very  rapid  and  the  tubes 
being  nearly  vertical  do  not  collect  much  scale. 

These  two  facts  have   made  this  boiler  work  satisfactorily 


I)  PES    OF    BOILERS. 


27 


with  bad  feed-water  when  some  other  types  of  boiler  would  not 
answer  at  all. 

The  water-level  is  not  the  same  in  all  three  drums  when  the 
boiler  is  working.  The  front  drum  will  show  a  level  6  inches 
higher  than  the  rear  drum  if  the  boiler  is  forced  hard. 

Water  Tube  Marine  Boilers.— With  the  advent  of  very 
high  steam  pressures  on  steamships  there  has  been  a  tendency 
to  replace  the  Scotch  boiler  by  some  form  of.water-tube  boiler. 

The  objects  that  are  sought  in  water-tube  boilers  for  steam- 
ships are  a  larger  power  for  the  weight  and  the  ability  to  carry 
high  pressures. 

It  is  still  a  question  whether  the  water-tube  boiler  will  or 
can  replace  the  Scotch  boiler. 


Fig.  17. 

Babcock  and  Wilcox  Marine  Type.— This  boiler,  shown 
by  Fig.  17,  is  made  up  of  sections  connected  at  one  end  to  the 


28  STEAM-BOILERS. 

bottom  of  a  drum  running  at  right  angles  to  the  tubes,  and  at  the 
other  end  to  a  tube  leading  into  the  side  of  the  drum  at  the  level 
of  the  water-line.  The  side  sections  are  continued  down  to  the 
level  of  the  grate,  the  tubes  being  replaced  by  forged  steel  boxes 
of  6-inch  square  sections  at  the  furnace  sides.  These  boxes  are 
located  one  above  the  other  on  the  same  angle  as  the  tubes;  they 
take  the  place  of  brickwork,  insure  a  cool  side  casing,  and  prevent 
the  adherence  of  clinkers. 

Placed  across  the  bottoms  of  the  front  header  ends  and  con- 
nected with  them  by  4-inch  tubes  is  a  forged  steel  box  of  6-inch 
square  section. 

This  box  is  situated  at  the  lowest  corner  of  the  bank  of  tubes 
and  forms  a  blow-off  connection  or  mud-drum,  through  which 
the  boiler  may  be  completely  drained. 

The  circulation  of  wrater  in  the  tubes  is  from  the  front  to  the 
back,  w"here  the  connecting-tube  leading  from  each  section  to 
the  drum  discharges  a  mixture  of  steam  and  water  against  the 
baffle  in  the  large  drum. 

Hie  path  of  the  gases  is  shown  by  the  arrows. 

The  Belleville  Boiler  is  represented  by  Fig.  18;  it  con- 
sists essentially  of  a  series  of  coils  of  pipe  made  up  with  bends 
and  elbows  around  which  the  products  of  combustion  pass 
on  the  way  to  the  chimney.  At  the  top  there  is  a  steam-drum 
A,  connected  by  two  circulating-pipes  B  and  C,  with  a  drum 
D  at  the  bottom.  From  the  mud-drum  D  a  rectangular  feed- 
supply  runs  across  the  front  of  the  boiler  to  all  the  coils  or 
elements  of  the  boiler.  Each  element  is  continuous  from  the 
feed-supply  to  the  steam-drum,  and  is  made  up  of  slightly 
inclined  pieces  of  pipe  with  horizontal  bends  or  connections 
at  the  end.  The  effect  is  much  as  though  a  helical  coil  were 
flattened  into  two  vertical  tiers  of  pipes.  The  amount  of 
water  in  the  boiler  is  so  small  that  it  cannot  be  run  without 
an  automatic  feed-water  regulator,  which  in  turn  requires  the 
attention  of  an  expert  feed-water  tender.  The  several  ele- 
ments deliver  a  mixture  of  water  and  steam  to   the  steam- 


TYPES    OF  BOILERS. 


29 


3° 


STEAM-BOILERS. 


drum,  which  does  not  appear  to  act  efficiently  as  a  separator, 
as  an  external  separator  is  placed  between  the  boiler  and  the 
engine.  The  feed-water  is  supplied  to  the  steam-drum  and 
passes  through  the  external  circulating-pipes  to  the  mud-drum, 
where  it  deposits  much  of  its  impurities. 

Thornycroft  Boiler. — The  boiler  represented  by  Figs.  19 
and  20  was  built  for  the  torpedo-boat  destroyer,  "Daring," 
by  Mr.  Thornycroft;  boilers  of  slightly  different  forms  have 
been  fitted  by  him,  in  torpedo-boats  and  steam-launches. 

The  boiler  consists  essentially  of  a  large  drum  or  separator 
at  the  top  and  three  drums  at  the  bottom,  connected  by  a  large 
number  of  bent-tubes.  There  is,  inside  of  the  casing,  a  large 
tube  connecting  the  top  drum  to  the  middle  drum  at  the  bottom, 
and  this  drum  is  connected  to  the  side  drums  by  smaller  pipes. 
The  circulation  is  down  from  the  top  drum  to  the  middle  lower 
drum,  and  from  that  to  the  side  drums,  then  up  through  all  the 
bent  water-tubes  to  the  upper  drum,  where  mingled  water  and 
steam  is  delivered  against  a  baffle-plate  above  the  water-line. 
Steam  is  drawn  from  a  nozzle  at  the  front  end  of  the  top 
drum. 

The  arrangement  of  grates  and  fire-doors  is  shown  in 
elevation  and  section  by  Fig.  19.  The  middle  drum  divides 
the  grate  into  two  parts;  over  that  drum  is  a  space  which  is 
in  communication  with  the  uptake,  as  shown  by  Fig.  20. 
The  products  of  combustion  pass  among  the  tubes  leading 
from  the  middle  drum;  the  tubes  to  the  outer  drums  intercept 
the  radiant  heat  which  would  otherwise  strike  on  the  boiler- 
casing. 

The  boiler-setting  is  an  iron  frame,  and  the  casing  is  thin 
plate  iron  lined  with  incombustible  non-conducting  material. 
There  are  numerous  doors  through  the  casing  for  cleaning  the 
tubes. 

This  boiler  has  proved  very  successful  with  a  forced 
draught,  making  steam  freely  and  giving  little  trouble.  The 
boiler  contains  so  small  an  amount  of  water  that  steam  may 


TYPES  OF  BOILERS. 


31 


STEAM-BOILERS. 


be  raised  quickly,  and  any  demand  for  steam  can  be  quickly 
met.  On  the  other  hand,  the  feed-supply  must  be  regulated 
with  care  and  skill,  and  the  pressure  is  liable  to  fluctuate. 


Fig 


The  Yarrow  Boiler. — The  form  of  boiler  used  by  Mr. 
Yarrow  for  torpedo-boats,  is  shown  by  Fig.  21.  It  resem- 
bles  in    general   arrangement    a  form    used    by    Mr.  Thorny- 


TYPES   OF   BOILERS 


33 


croft  with  one  grate.  It,  however,  differs  radically  in  certain 
particulars,  namely,  in  that  the  tubes  are  straight  and  that 
they  enter  the  upper  drum  below  the  water-line,  and  in  that 
there  are  no  pipes  outside  the  casing  to  carry  water  from  the 
upper  drum  to  the  lower  drum  or  reservoirs.  Some  of  the 
tubes  deliver  water  and  steam  to  the  upper  drum,  from  which 
steam  is  drawn ;  other  tubes  carry  water  from  the  upper 
drum  to  the  lower  drums.  A  given  tube  may  act  sometimes 
in  one  way  and  sometimes  in  the  other.  Naturally  those 
tubes  which  receive  the  most  heat  and  make  the  most  steam 
deliver  to  the  upper  drum,  and  tubes  that  receive  less  heat 
carry  down  water. 

The  air   for  the   fire   is  drawn    from   an  iron  box  or  ca>ing 
outside  the   boiler-casing,  so   that  the   heat  escaping  from  the 
boiler-casing  is   largely  carried  back   to   the   fire,  and  the  fire 
room,  and  also  the  rest  of  the  vessel,  is  heated  up  less. 

The  Almy  Boiler. — This  boiler,  which  is  represented  by 
Fig.  22,  is  made  of  short  lengths  of  pipe  screwed  into  return- 
bends  and  into  twin  unions.  At  the  bottom  is  a  large  tube  or 
pipe  forming  three  sides  of  a  square  at  the  sides  and  back  of 
the  grate.  From  this  water-space  the  tubes  lead  into  a  similar 
structure  at  the  top.  The  steam  and  water  are  discharged  into 
a  separator  in  front  of  the  boiler,  from  which  steam  is  drawn; 
while  the  water  separated  therefrom,  together  with  the  feed- 
water,  passes  down  through  circulating-pipes  to  the  bottom  of 
the  boiler. 

The  boiler  is  provided  with  a  coil  feed-water  heater  above 
the  main  boiler.  It  is  enclosed  by  a  casing  lined  with  non- 
conducting material.     It  is  intended  for  general  marine  work. 

General   Discussion. — In  deciding  on  the  type  of  boiler  to 
be  selected  for  any  particular  case  there  are  a  number  of  things 
to  be  considered.     The  following  are  the  most  important: 
i.  The  pressure  to  be  carried. 
2.  The  quality  of  the  feed-water. 


34 


STEAM-BOILERS. 


The  variation  in  load. 
The  size  of  the  battery. 
The  amount  of  land  available. 
The  cost  of  land. 
The  fuel  to  be  used. 
In  general,  it  may  be  said  that  the  more  simple  the  boiler  is, 
the  better  it  is;    that  all  parts  of  the  boiler  should  be  easily 


Fig.  22. 


accessible,  and  that  the  boiler  should  be  so  designed  that  it  will 
not  strain  itself  by  unequal  expansion. 

The  thickness  of  the  steel  needed  in  the  shell  of  a  boiler  must 
increase  as  the  pressure  increases,  and  also  as  the  diameter 
increases,  as  will  be  shown  later.     It  is  not  considered  advisable 


TYPES    OF    BOILERS. 


35 


to  transmit  heat  through  plates  over  one  half  an  inch  in  thick- 
ness. 

For  high  pressures  this  means  that  if  shell  boilers,  like  Figs.  I 
and  2,  are  to  be  used  the  diameter  must  not  be  greater  than 
60  or  66  inches,  thus  limiting  the  horse-power  of  a  single  unit 
to  from  80  to  125  boiler  horse-power,  depending  on  the  kind  of 
coal  used  and  the  rate  of  combustion. 

This  type  of  boiler  is  the  least  expensive,  and  if  there  were 
ample  room  and  if  the  land  occupied  were  inexpensive,  it  might 
be  advisable  to  instal  a  large  number  of  these  small  units  to 
make  up  the  horse-power  desired.  If,  however,  land  were  ex- 
pensive, or  if  there  were  but  a  small  amount  of  land  available, 
then  this  type  could  not  be  considered. 

A  vertical  boiler,  like  the  Manning,  or  some  form  of  water- 
tube  boiler,  like  the  Babcock  and  Wilcox,  the  Heine,  or  the 
Stirling,  would  probably  be  selected. 

If  the  cost  of  land  were  extremely  high  water-tube  boilers 
might  be  located  on  the  second,  third,  and  fourth  floors  of  a  build- 
ing and  discharge  steam  into  a  common  main  supplying  engines 
in  the  basement.  This  arrangement  is  common  in  power-  and 
lighting-stations  located  in  the  middle  of  a  city. 

There  is  no  difficulty  in  making  a  building  sufficiently  strong 
to  carry  the  weights. 

There  should  be  a  sufficient  number  of  boilers  in  the  batterv, 
so  that  one  could  be  shut  down  and  the  others  carry  the  load. 
As  a  boiler  can  be  run  from  25  to  30  per  cent  over  its  rated 
capacity  this  means  that  there  should  be  at  least  four  boilers 
in  the  battery  if  the  plant  is  to  run  continuously.  It  is  not  cus- 
tomary to  install  units  of  more  than  350  or  500  horse-power  even 
in  the  largest  batteries. 

The  quality  of  the  feed-water  must  also  be  considered  in 
deciding  how  many  boilers  there  are  to  be  in  the  battery.  If 
the  feed-water  Is  very  bad  it  may  be  necessary  at  times  to  have 
two  boilers  shut  off  from  the  line.  More  boilers  are  needed  when 
the  feed-water  is  of  poor  quality,  not  only  for  the  reason  mentioned, 


q6  STEAM-BOILERS. 

but  also  because  of  the  poorer  efficiency  of  the  heating-surface 
due  to  deposits  of  scale. 

The  heating  value  of  the  fuel  also  enters  as  a  factor  in  deter- 
mining the  number  of  boilers  needed. 

If  a  steady  pressure  is  to  be  maintained  with  as  little  fluctua- 
tion as  possible,  a  boiler  with  a  large  water-space  should  be 
chosen.  Such  a  boiler  will  meet  a  sudden  demand  for  steam 
without  much  drop  in  pressure;  on  the  other  hand,  it  takes  a 
long  time  to  increase  the  pressure. 

The  Scotch  boiler  and  a  modification  of  the  same  having  the 
combustion-chamber  in  a  space  bricked  in  at  the  end  of  the 
boiler  have  been  used  successfully  for  the  operation  of  draw- 
bridges, where  the  demand  for- steam  is  at  the  rate  of  ioo  boiler 
horse-power  for  a  period  of  from  five  to  eight  minutes  two  or 
three  times  an  hour. 

The  cost  of  boilers  varies  with  the  price  of  steel.  At  the 
present  time,  1908,  horizontal  multitubular  boilers  cost,  when 
set,  about  $11.50  per  horse-power  for  boilers  60  to  66  inches  in 
diameter. 

Water-tube  boilers  about  200  horse-power  per  unit  cost  from 
$15.50  to  $16.50  per  horse-power,  set  ready  to  connect  to  the 
steam-main. 

Scotch  boilers  cost  about  $16.50  per  horse-power  in  sizes 
ranging  from  100  to  150  horse-power. 

Tables  giving  the  diameters,  ratings,  width,  length,  and 
heights  of  settings  of  many  of  the  common  types  of  boilers  have 
been  added  to  the  appendix. 

We  believe  that  these  tables  will  be  useful  to  any  one  who 
may  be  making  the  preliminary  design  of  a  boiler  plant. 


CHAPTER  IT. 

SUPERHEATERS. 

Steam  may  be  dry  and  saturated,  primed  or  superheated. 

Dry  and  saturated  steam  and  primed  or  <;wet"  steam,  as  it 
is  sometimes  called,  at  the  same  pressure  have  the  same  tem- 
perature. 

As  bubbles  of  steam  break  through  the  surface  of  the  water 
in  a  boiler  some  water  is  atomized  into  the  steam-space  where  it 
floats  just  as  moisture  floats  in  the  air. 

The  amount  by  weight  of  such  water  floating  in  a  total  weight 
of  one  pound  is  called  the  priming.  This  priming  is  in  certain 
types  of  boilers  between  .005  and  .03. 

If  heat  is  now  added  to  the  wet  steam  in  the  steam-space 
the  water  floating  in  the  steam  will  vaporize  and  at  the  instant 
when  all  of  this  water  has  vaporized  we  have*  dry  and  saturated 
steam.  If  more  heat  is  added  the  temperature  of  the  steam  will 
go  up  and  the  steam  will  become  superheated;  the  amount  of 
superheating  in  degrees  being  the  difference  between  the  tem- 
perature of  the  steam  as  observed  and  that  of  saturated  steam 
of  the  same  pressure. 

The  specific  heat  of  superheated  steam  is  the  amount  of  heat 
necessary  to  raise  the  temperature  of  one  pound  of  superheated 
steam  i°  Fahrenheit. 

The  specific  heat  has  been  found  to  increase  with  the  pressure 
of  the  steam,  and  at  any  constant  pressure  to  decrease  as  the 
number  of  degrees  of  superheating  increases. 

37 


STEAM-BOILERS. 


The  following  table  from  the  experiments  of  Thomas  and 
Short  gives  the  mean  value  of  the  specific  heat  for  different 
pressures  and  different  degrees  of  superheat. 


SPECIFIC  HEAT  OF  SUPERHEATED  STEAM. 


Pressure  Lbs.  Sq.  In. 

Absolute. 

Degrees  of 
Superheat. 

6 

13 

3° 

50 

100 

200 

300 

20° 

.536 

•547 

•553 

.571 

•593 

.621 

.649 

50 

.522 

•S32 

•  542 

•555 

•575 

.600 

.621 

IOO 

.503 

•512 

•524 

•537 

•557 

.581 

•599 

15° 

.486 

.496 

.508 

•522 

-544 

•567 

.585 

200 

•471 

.480 

-494 

•5°9 

-533 

.556 

•574 

250 

•  456 

.466 

.481 

•  496 

.522 

.546 

•  564 

300 

.442 

•453 

.468 

.4S4 

.511 

•537 

•554 

Attached  Superheater. — There  are  two  classes  of  super- 
heaters, the  attached  and  the  independently  fired. 

The  attached  is  connected  to  the  boiler,  receives  its  heat  from 
the  fire  under  the  boiler,  and  in  general  does  not  give  more  than 
150  degrees  of  superheat. 

Nearly  all  of  the  attached  superheaters  are  connected  to  the 
steam  and  to  the  water-space  of  the  boiler  in  such  a  way  that 
they  can  be  flooded  while  steam  is  being  gotten  up  in  the  boiler. 

Some  makes  of  attached  superheaters  may  be  flooded  and 
the  heating-surface  used  as  additional  steam-generating  surface 
when  the  boiler  is  delivering  saturated  steam. 

Babcock  and  Wilcox  Attached  Superheater. — This 
superheater  is  shown  by  Fig.  23.  It  is  located  directly  under 
the  drums  between  the  first  and  second  gas  passages.  It  is  made 
of  bent  fubes  expanded  into  steel  headers,  as  shown. 

Steam  is  taken  from  the  dry  pipe  in  the  top  of  each  drum 
into  the  center  of  the  top  headers,  and  after  passing  through  the 
tubes  leaves  at  the  outer  end  of  the  bottom  header.     From  the 


SUPERHEATERS. 


39 


end  of  the  bottom  header  a  pipe  leads  up  to  a  nozzle  fastened  to 
the  drum  of  the  boiler,  but  not  connecting  with  the  drum.  In 
some  instances  these  superheaters  have  been  arranged  to  work 


Fig.  23. 


flooded  with  water  when  the  boiler  was  not  delivering  superheated 
steam. 

Heine  Attached  Superheater. — Fig.  24  and  the  two 
cross-sections  shown  on  the  same  cut  gives  the  arrangement  of 
the  Heine  superheater. 

The  greater  part  of  the  products  of  combustion  is  made  to 
circulate,  as  shown  by  the  dotted  arrows,  and  is  utilized  in  generat- 
ing steam. 

A  small  part  of  the  products  of  combustion  is  made  to  follow 
the  path  shown  by  the  full  arrows,  and  pass  through  the  super- 
heater. The  path  of  these  gases  will  be  made  clear  by  the  sec- 
tions BB  and  A  A. 

Stirling  Attached  Superheater.— The  attached  super- 
heater is  shown  as  the  middle  bank  of  small  tubes  in  Fie.  2Z. 
The  detail  of  this  superheater  is  shown  by  Fig.  26,  which  is  a 
cross-section  taken  through  Fig.  25. 


4o 


STEAM-BOILERS. 


SUPERHEATERS. 


41 


Saturated  steam  from  the  front  and  rear  drums  enters  the  left- 
hand  section  of  the  upper  drum  (Fig.  26)  through  the-  holes  shown 
near  the  top.     This  steam  circulates  through  the  tubes  to  and 


Fig.  25. 


from  the  lower  drum,  as  shown  by  the  arrows,  and  is  drawn  off 
at  the  right-hand  end  of  the  upper  drum. 

There  is  a  removable  diaphragm  in  the  lower  drum  and  covers 
in  the  two  diaphragms  in  the  upper  drum.     These  are  provided 


42 


STEAM-BOILERS. 


so  as  to  make  it  possible  for  a  man  to  get  at  the  ends  of  any  tubes 
which  may  need  to  be  re-expanded. 

When  using  saturated  steam  the  two  by-pass  valves  in  the 
diaphragms  in  the  upper  drum  are  opened  and  the  lower  drum 


Fig.  26. 

is  connected  with  the  bottom  of  one  of  the  other  drums  through 
valves  and  piping  provided  for  flooding. 

Independently -fired  Superheater. — The  independently- 
fired  superheaters  are  intended  to  give  higher  temperatures  to 
the  steam  than  can  be  obtained  by  an  attached  superheater. 


SUPERHEATERS. 


43 


Superheaters  of  this  class  give  a  thermal  efficiency  of  about 
60  per  cent.  Different  makers  use  different  amounts  of  heating- 
surface  for  the  same  capacity  and  the  same  degrees  of  superheat- 
ing. It  seems  that  about  3  square  feet  are  needed  per  boiler 
horse-power  if  the  steam  is  to  leave  at  about  6oo°  F.  and  was  not 
primed  more  than  one  per  cent  on  entrance  to  the  superheater. 

In  order  to  keep  the  temperature  of  the  superheated  steam  as 
uniform  as  possible  it  is  customary  to  make  use  of  a  Dutch  oven 
furnace,  a  furnace  with  a  fire-brick  arch  over  the  grate.  This 
arch,  by  giving  up  heat  at  one  time  and  by  absorbing  heat  at 
another  time,  tends  to  keep  the  gases  more  nearly  at  a  uniform 
temperature. 

Foster  Independently- fired  Superheater. — This  is 
shown  in  longitudinal  view  by  Fig.  27.    Fig.  28  gives  a  section 


Fig.  27. 


through  a  tube  and  header  and  shows  the  cast-iron  rings  put  on 
to  give  additional  surface  for  absorbing  heat,  and  also  to  prevent 
any  rapid  fluctuations  in  the  temperature  of  the  fire  affecting  the 
temperature  of  the  steam. 


44 


STEAM-BOILERS. 


The  inner  tube  shown  in  this  cut  is  sometimes  closed  together 
at  the  ends  but  not  tightly  sealed.  This  tube,  which  is  held  in 
place  by  distance  pieces  in  the  shape  of  rivet-heads,  causes  the 


Mm 


Fig.  28. 


steam  to  flow  rapidly  through  the  annular  space  between  it  and 
the  outer  tube. 

The  steam  enters  Fig.  27  at  the  top  and  leaves  at  the  bottom. 

American  Independently-fired  Superheater. — The 
American  superheater  is  shown  by  Fig.  29.  Like  the  preceding 
it  is  built  with  a  Dutch  oven-furnace. 

A  "tempering"  door  located  in  the  bridge-wall  may  also  be 
used  for  regulating  the  temperature  of  the  gases. 

The  superheater  is  made  up  of  headers,  which  are  steel  cast- 
ings joined  together  by  steel  tubes.  The  tubes  from  the  bottom 
of  one  header  enter  the  top  of  the  header  opposite.  The  steam 
circulates  as  many  times  as  there  are  headers  in  one  row  and 
passes  out  at  the  bottom. 

The  bottom  tubes  are  of  Shelby  drawn  nickel-steel  and  in 
some  cases  are  covered  with  tile  or  cast  iron. 

The  headers  are  supported  one  on  top  of  another  with  steel 
balls  in  between.  These  balls  provide  for  the  expansion  of  the 
tubes. 


SUPERHEATERS. 


45 


I 


46  STEAM-BOILERS. 

A  superheater  of  this  make,  installed  at  the  Massachusetts 
Institute  of  Technology,  designed  to  superheat  10,000  pounds 
of  steam  an  hour  at  250  pounds  pressure  with  one  per  cent  prim- 
ing, 25o°F.,  had  a  grate-area  of  15.6  square  feet  and  558.3  square 
feet  of  heating-surface. 

Steam  Pipe-fittings  for  Superheated  Steam. — Steel 
castings  are  probably  the  best  fittings  to  use  on  pipe  lines  carry- 
ing highly  superheated  steam.  Steel  fittings  are  expensive  and 
are  not  to  be  found  in  stock. 

There  is  evidence  tending  to  show  that  cast  iron,  especially 
if  of  a  poor  grade,  is  affected  in  its  strength  by  superheated  steam; 
there  is  no  evidence,  however,  showing  that  gun-iron  fittings 
have  deteriorated  under  the  action  of  superheated  steam. 

Fittings  on  superheated  steam  lines  are  subjected  to  greater 
strains  on  account  of  the  larger  amount  of  expansion  of  the 
pipe  and  on  account  of  the  greater  changes  in  temperature. 

Composition  loses  its  strength  at  high  temperatures  and  is 
unsafe  to  use  with  superheated  steam. 


CHAPTER   III. 
FUELS   AND   COMBUSTION. 

The  fuels  used  for  making  steam  are  coal,  coke,  wood, 
charcoal,  peat,  mineral  oil,  and  natural  and  artificial  gas. 
Various  waste  and  refuse  products,  such  as  straw,  sawdust, 
and  bagasse,  are  burned  to  make  steam. 

All  coals  appear  to  be  derived  from  vegetable  origin,  and 
they  owe  their  differences  to  the  varying  conditions  under 
which  they  were  formed  or  to  the  geological  changes  which 
they  have  undergone. 

Anthracite  Coal  consists  almost  entirely  of  carbon  and 
inorganic  matters;  it  contains  little  if  any  hydrocarbon. 
Some  varieties,  for  example  certain  coals  found  in  Rhode 
Island,  appear  to  approach  graphite  in  their  characteristics, 
and  are  burned  with  difficulty  unless  mixed  with  other  coals. 
Good  anthracite  is  hard,  compact,  and  lustrous,  and  gives  a 
vitreous  fracture  when  broken.  It  burns  with  very  little 
flame  unless  it  is  moist,  and  gives  a  very  intense  fire,  free 
from  smoke.  Even  when  carefully  used,  it  is  liable  to  break 
up  under  the  influence  of  the  high  temperature  of  the  furnace 
when  freshly  fired,  and  the  fine  pieces  may  be  lost  with  the 
ash. 

Semi-anthracite  or  Semi-bituminous  Coal  is  intermedi- 
ate in  its  properties  between  anthracite  coal  and  bituminous 
coal;  it  contains  some  hydrocarbon,  is  less  dense  than  anthra- 
cite, it  breaks  with  a  lamellar  fracture,  and  it  burns  readily 
with  a  short  flame. 

47 


48  STEAM-BOILERS. 

Bituminous  Coals  contain  a  large  and  varying  per  cent 
of  hydrocarbons  or  bituminous  matter.  Their  physical  prop- 
erties and  behavior  when  burning,  vary  widely  and  with  all 
intermediate  gradations  represented,  so  that  classification  is 
difficult.  Three  kinds  may.  however,  be  distinguished,  as 
follows  : 

Dry  bituminous  coals,  which  burn  freely  and  with  little 
smoke  and  without  caking 

Caking  bituminous  coals,  which  swell  up,  become  pasty, 
and  cake  together  in  burning.  They  are  advantageously  used 
for  gas-making. 

Long-flaming  bituminous  coals,  which  have  a  strong  ten- 
dency to  produce  smoke ;  some  do  and  some  do  not  cake 
while  burning. 

Coke  is  made  from  bituminous  and  semi-bituminous  coal 
bv  driving  off  the  hydrocarbons  by  heat.  Coke  made  as  a 
by-product  in  gas  retorts,  is  weak  and  friable,  and  has  little 
value  for  making  steam.  Coke  made  in  coking  ovens,  by 
partial  combustion  of  the  coal  which  is  coked,  is  of  a  dark- 
gray  color,  porous,  hard,  and  brittle.  It  has  a  metallic  lustre, 
and  gives  out  a  slight  ringing  sound  when  struck.  Sulphur 
in  the  coal  may  be  burned  out  in  coking,  if  the  coal  is  moist 
or  if  steam  is  supplied  during  coking,  so  that  coke  may  be 
comparatively  free  from  this  noxious  element  even  when  made 
from  a  poor  coal.  Coke  burns  without  flame  and  makes  a 
fierce  fire  when  forced. 

Lignite,  or  brown  coal,  is  of  more  recent  geological 
formation  than  coal,  and  is  in  a  manner  intermediate  between 
coal  and  peat.  It  frequently  contains  much  moisture  and 
mineral  matter.  It  is  used  where  good  coal  is  difficult  to  get, 
and  while  the  better  varieties  form  a  useful  fuel,  the  poorer 
qualities  have  little  value. 

Peat,  or  turf,  is  obtained  from  bogs.  It  consists  of 
slightly  decayed  roots  of  the  swamp  vegetation  mingled  with 
more  or  less  earthy  matter.      For  domestic  use  it  is  cut  and 


FUELS   AND    COMBUSTION.  49 

dried  in  the  air.  It  is  little  used  for  making  steam,  though 
when  pulverized,  dried,  and  compressed  it  makes  a  useful 
artificial  fuel. 

Wood  is  used  for  making  steam  either  in  remote  places 
where  coal  is  hard  to  get  and  timber  is  plenty,  or  where  saw- 
dust or  other  refuse  wood  is  produced  in  quantity  in  manufac- 
turing operations.  Wood  is  also  used  for  kindling  coal-fires. 
One  cord  of  hard  wood  is  equivalent  to  one  ton  of  anthracite 
coal;  one  cord  of  yellow-pine  is  equal  to  half  a  ton  of  coal; 
other  soft  woods  are,  as  a  rule,  of  less  value  for  fuel. 

Charcoal  is  made  by  charring  wood ;  it  is  but  little  used 
for  making  steam. 

Mineral  Oil,  in  the  form  of  crude  petroleum  or  the  refuse 
heavy  oil  left  from  the  distillation  of  petroleum,  is  used  for 
making  steam,  especially  in  the  neighborhood  of  the  Black 
Sea  oil-field,  and  by  steamers  carrying  oil  from  those  fields. 
It  is  customary  to  throw  the  oil  into  the  furnace  in  the  form 
of  finely  divided  spray  through  special  spraying  apparatus 
worked  either  with  compressed  air  or  with  superheated  steam. 
The  use  of  superheated  steam  has  its  convenience  only  to 
recommend  it,  for  it  adds  to  the  inert  material  to  be  uselessly 
heated.  Special  precautions  must  be  taken,  when  petroleum 
is  burned,  to  avoid  flooding  the  furnace  with  oil  and  to  pre- 
vent explosions  of  the  vapor  and  burning  of  the  oil  in  tanks 
or  receptacles. 

Gases. — Natural  gas  from  gas-wells  has  been  used  for 
making  steam,  usually  in  a  crude  and  wasteful  way.  Some 
attempts  have  been  made  to  use  gas  made  from  poor  and 
smoky  coal,  in  producer-furnaces  like  those  used  in  metallurgi- 
cal operations;  but  the  gain  to  be  expected  is  only  the  sup- 
pression of  the  smoke  nuisance,  which  is  rather  a  social  than 
an  economical  problem. 

Artificial  Fuels. — The  small  waste  from  coals  and  char- 
coals, sawdust,  and  other  fine  combustible  material  which 
cannot  be  sold  in  such  shape,  is  sometimes  made  into  cakes  or 


5° 


S  TEA  M-BOILERS. 


briquettes  by  mixing  it  with  some  adhesive  material  and  then 
compressing  it.  The  adhesive  materials  have  been  wood-tar, 
coal-tar,  or  else  clay.  Tar  is  available  in  limited  quantities 
only,  and  clay  is  disadvantageous  since  it  adds  to  the  inert 
material,  of  which  fine  fuel  is  liable  to  have  an  excess. 
Artificial  fuels  have  some  advantages  for  special  purposes,  and 
can  be  stored  compactly ;  they  are  used  mostly  where  good 
fuel  is  difficult  to  get. 

Composition  of  Fuels. — The  composition  of  a  number 
of  American  coals,  together  with  the  total  heat  of  combustion 
by  William's  bomb,  is  given  in  the  table  on  page  51,  which 
has  been  kindly  furnished  by  Mr.  Henry  J.  Williams.  These 
results  are  a  part  of  a  very  extended  investigation  by  Mr. 
Williams,  to  be  published  in  full  in  the  near  future.  Most 
of  the  results  are  the  averages  of  several  separate  analyses,  and 
all  may  be  depended  upon  to  give  a  fair  representation  of  the 
coals  named. 

Analyses  by  Mahler  of  various  European  coals  and  of  a 
few  American  coals,  together  with  the  total  heat  of  combus- 
tion, are  given  in  the  table  on  page  52. 

The  following  table  gives  the  composition  of  several  rep- 
resentative petroleums : 

COMPOSITION    OF    PETROLEUMS. 


Pennsylvania,  crude 

Caucasian,  light.  .  . . 

heavy   . . 

Petroleum  refuse. .  . 


Carbon. 


84.9 
S6.3 
S6.6 
87.1 


Hydrogen. 

»3 

7 

13 

6 

12 

3 

11 

7 

Oxygen. 


i-4 

0.1 

1. 1 

1 .2 


Specific 
Gravity. 


0.8S6 
0.884 
0.938 
0.93S 


Heat  of  Combustion. — The  number  of  thermal  units  de- 
veloped by  the  complete  combustion  of  one  unit  of  weight  of 
a  fuel  is  called  the  heat  of  combustion.  It  can  be  determined 
by  burning  the  fuel  in  a  properly  constructed  calorimeter. 
The  most  recent  and  best  results  are  those  obtained  by  the 
use  of  Mahler's  bomb-calorimeter.      This  is  a  strong  recep- 


FUELS    AND    COMBUSTION. 


51 


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FUELS   AND    COMBUSTION. 


^ 


tacle  of  wrought  iron  or  bronze,  gold-plated  or  enamelled 
inside.  The  fuel  to  be  tested  is  placed  in  a  small  platinum 
crucible,  with  an  arrangement  for  igniting  by  electricity. 
The  bomb  is  then  filled  with  oxygen  under  the  pressure 
of  about  twenty-five  atmospheres,  and  is  placed  in  a  calo- 
rimeter-can containing  water.  There  is  oxygen  in  excess,  so 
that  the  charge  when  ignited  is  completely  consumed,  and 
the  resultant  total  heat  of  combustion  is  absorbed  by  the 
metal  of  the  bomb  and  by  the  water  in  the  calorimeter.  The 
corrections  for  the  calorimeter  are  determined  by  burning  in 
it,  some  substance  like  naphthaline,  for  which  the  heat  of  com- 
bustion is  known.  The  processes  of  making  combustion 
determinations  are  simple  and  direct;  the  difficulties  are  those 
incident  to  accurate  measurements  of  temperatures,  for  which 
purpose  the  best  physical  thermometers  are  required.  The 
experimenter  must  be  an  expert  physicist,  who  has  had  expe- 
rience in  the  use  of  the  apparatus.  The  table  of  composi- 
tion of  fuels  by  Mahler  *  gives  also  the  total  heats  of  the 
fuels,  determined  by  the  same  experimenter  by  aid  of  the 
bomb-calorimeter. 

An  engineering  expert  who  has  had  adequate  training  in 
a  physical  laboratory,  may  learn  how  to  make  determinations 
of  the  total  heat  of  combustion  ;  an  engineer  in  general  prac- 
tice will  find  it  advantageous  to  refer  such  work  to  an  expert 
physicist.  It  is  not  too  much,  to  say  that  all  crude  forms  of 
apparatus  for  finding  total  heat  of  combustion  of  fuels  are 
useless  and  misleading. 

The  heats  of  combustion  of  carbon  in  various  forms  as  de- 
termined by  Berthelot  f  are  : 

Diamond    7^59     calories. 

Diamond  bort 7860.9       " 

Graphite 790 1.2        " 

Amorphous  from  wood 8137.4       " 

*  Bulletin  de  la  Soc.  d'Encouragement  pour  Industrie  nationale,  1891. 
+  Comptes  rendu, -1889. 


54  5  TEA  M-BOILERS. 

The  heat  of  combustion  of  carbon  in  fuels  may  be  taken  at 
8140  calories,  a  calorie  being  defined  as  the  heat  required 
to  raise  one  kilogram  of  water  from  I5°C  to  160  C.  This 
will  give  in  the  English  system  of  units  14650  British  thermal 
units,  the  B.  T.  U.  being  defined  as  the  heat  required  to  raise 
the  temperature  of  a  pound  of  water  from  62°  F.  to  630  F. 
These  definitions  are  founded  on  Rowland's  determination  of 
the  mechanic  equivalent  of  heat ;  the  difference  between  them 
and  others  commonly  given  are  not  of  practical  importance 
in  this  connection. 

The  following  table  gives  the  heat  of  combustion  of  some 
elements  and  simple  gases : 

Carbon  burned  to  C02 8, 140  calories  ;  14,650  B.T.  U. 

Carbon  burned  to  CO 4,400  " 

Hydrogen 34, 500          "  62,100  " 

Sulphur , 4,032  " 

Marsh-gas,  CH4 23,513 

Olefiant  gas,  C,H, 21,343  " 

Carbon  monoxide 10,250  " 

Chemistry  of  Combustion.— Calculations  concerning  the 
heat  of  combustion  of  fuels  and  the  amount  of  air  needed  for 
combustion,  require  a  knowledge  of  the  elements  of  chemistry. 

Elementary  chemical  substances  are  those  that  have  not 
been  decomposed,  such  as  oxygen,  hydrogen,  and  nitrogen. 
The  elements  enter  into  chemical  combination  in  fixed  propor- 
tions by  weight ;  these  proportions  are  called  the  combining 
weights  or  the  atomic  weights  of  the  elements.  In  the  following 
table  are  given  the  most  important  chemical  elements  of  fuels, 
their  chemical  symbols,  and  their  atomic  weights.  The  table 
gives  other  useful  information  which  will  be  referred  to  later. 

A  chemical  combination,  such  as  water,  is  represented  by 
a  formula  consisting  of  the  symbols  of  the  elements  entering 
into  the  combination,  each  symbol  having  a  subscript  which 
shows  the  number  of  times  the  combining  or  atomic  weight  of 


FUELS  AND    COMBUSTION. 


55 


iSj|mbol  or 
Lomposi- 


Carbon 

Hydrogen 

Oxygen 

Nitrogen   

Sulphur   

Carbon  droxide  .  .  , 
Carbon  monoxide. 

Water   

Air 

Ash 


C 
H 

O 

N 

S 
CO, 
CO 
H,0 


Atomic  or 

Molecular 

Weight. 


12 
I 

16 

14 
32 
12  4-  2  X  16 
12  +  16 
2  +  16 


Specific 
Volumes. 


178.20 
II. 21 
12.74 

8.10 
12.81 

12.39 


Specific 

Heat  in 

Gaseous 

Condition 


3-409 

O.2175 

O.2438 

O.2169 

0.24=10 

0.48* 

0-2375 

0.2f 


Density  or 

Weight  of 

One  Cubic 

Foot. 


0.0055  r 
0.08928 
0.07837 

0.12345 
0.07806 

0.08071 


Superheated  steam. 


f  Solid  condition. 


the  element  occurs  in  the  combination.  This  water  is  repre- 
sented by 

H,0, 

which  indicates  that  water  is  made  up  of  two  portions  of  hy- 
drogen and  one  portion  of  oxygen.  It  is  commonly  said  that 
two  atoms  of  hydrogen  and  one  atom  of  oxygen  unite  to  form 
one  molecule  of  water.  As  the  atomic  weight  of  hydrogen  is  1 
and  the  atomic  weight  of  oxygen  is  16,  we  have  water  formed 
of  two  pounds  of  hydrogen  to  16  pounds  of  oxygen. 

Again,  carbon  may  unite  with  one  portion  of  oxygen  to 
form  carbon  monoxide  or  carbonic  oxide,  represented  by  CO ; 
or  carbon  may  unite  with  two  portions  of  oxygen  to  form 
carbon  dioxide  or  carbonic  acid,  represented  by  CO,.  Re- 
ferring to  the  table  on  page  54,  it  appears  that  the  complete 
combustion  to  CO,  gives  more  than  three  times  the  heat  ob- 
tained from  incomplete  combustion  to  CO.  But  the  resulting 
gas,  CO  may  be  burned  with  one  more  portion  of  oxygen,  and 
will  finally  form  CO,.  Assuming  that  the  double  process  will 
yield  the  same  amount  of  heat  per  pound  of  coal  as  is  ob- 
tained by  direct  combustion  to  CO,,  we  may  calculate  the 
heat  of  combustion  of  one  pound  of  carbon  monoxide  as  fol- 
lows : 


56  5  TEA  M-BOILERS. 

In  the  combustion  of  carbon  to  CO,  12  pounds  of  carbon 
unite  with  16  pounds  of  oxygen,  forming  28  pounds  of  CO, 
hence  one  pound  of  carbon  will  form 

l^ti6  =  2i  lbs.  Of  CO. 

12 

The  heat  developed  by  burning  these  2\  pounds  of  carbon 
monoxide,  under  our  assumption,  is 

14650  —  4400  =  10250  B.  T.  U., 

so  that  each  pound  of  carbon  monoxide  will  yield 

10250 -f-  2^  =  4393  B.  T.  U., 

as  given  in  the  table  on  page  54. 

The  complete  combustion  in  either  case  will  give 

12  -f-  2  X  16  . 

— — =  3f 

12 

pounds  of  carbon  dioxide  for  each  pound  of  carbon. 

Calculation  of  Heat  of  Combustion.— If  a  fuel  were  a 
mechanical  mixture  of  two  chemical  elements  such  as  carbon 
and  sulphur,  the  heat  of  combustion  could  obviously  be  found 
by  calculating  the  parts  separately  and  adding  the  results.  For 
example,  a  mixture  of  60  per  cent  carbon  and  40  per  cent 
sulphur  would  give 

0.60  X  14650  =     8790.0 
0.40  X    4032  =     16 12. 8 

10402.8  B.  T.  U. 

for  each  pound  of  the  mixture. 

Fuels,  as  a  rule,  contain  carbon  in  a  free  state,  and  various 
compounds  of  carbon  and  hydrogen,  and  compounds  of  carbon, 
hydrogen,  and  oxygen.  Now  the  rapid  union  of  chemical  ele- 
ments is  usually  accompanied  by  the  evolution  of  heat,  as  in 


FUELS   AND    COMB  US  J  JON. 


r; 


the  combustion  of  oxygen  and  hydrogen.  Conversely,  heal  is 
required  to  break  up  a  chemical  combination  Now  the  com- 
bustion of  a  fuel  is  a  complex  process,  involving  usually  some 
breaking  up  of  chemical  compounds  and  the  union  of  chemical 
elements  with  oxygen  ;  the  exact  nature  of  the  process  is  far 
from  certain  even  when  the  real  chemical  compounds  and  ele- 
ments of  which  the  fuel  is  composed  are  known.  As  a  rule  we 
know  only  the  final  analysis  of  the  fuel  and  do  not  know  the 
compounds  which  enter  into  it.  For  this  reason  the  only 
true  way  of  determining  total  heat  of  combustion  is  by  experi- 
ment. Nevertheless  it  is  customary  and  convenient  to  make 
a  calculation  of  the  total  heat  of  combustion  by  an  arbitrary 
method,  when  the  real  heat  of  combustion  of  a  fuel  has  not 
been  determined. 

Dulong  proposed  that  the  heat  of  combustion  should  be 
calculated  on  the  assumption  that  the  oxygen  in  the  fuel  and 
enough  hydrogen  to  unite  with  it  and  form  water,  could  be  set 
aside  as  inert,  and  that  the  remainder  of  the  hydrogen  and  all 
the  carbon  could  be  treated  as  free  elements.  From  the  com- 
position of  water  and  the  atomic  weights  of  hydrogen  and 
oxygen  it  is  clear  that  each  pound  of  oxygen  will  require 

2X1        i 


16  8 

of  a  pound  of  hydrogen.  Dulong*s  method  may  therefore  be 
expressed  by  the  equation 

Total  heat  =  14.650  C  -j-  62. 100  (H  —  £0) 

in  which  the  letters  C.  H,  and  O  represent  the  -weights  of  car- 
bon, hydrogen,  and  oxygen  in  one  pound  of  fuel.  No  con- 
fusion need  arise  because  the  letters  are  used  with  a  different 
significance  from  that  given  them  in  chemical  formula.  This 
equation  does  not  give  very  satisfactory  results. 


5©  STEAM-BOILERS. 

Mahler  has  proposed  an  empirical  formula  for  finding 
heats  of  combustions  which  in  French  units  is 

Total  heat  =  8140  C  -(-  34,500  H  —  300CM  O  -f-  N), 

in  which  C,  H,  O,  and  N  represent  the  weights  of  the  ele- 
ments carbon,  hydrogen,  oxygen,  and  nitrogen  in  a  kilogram 
of  fuel.     The  result  is  in  calories. 

In  English  units  Mahler's  equation  becomes 

Total  heat  =  14,650  C  -|-  62, 100  H  —  5400  (O  +  N), 

in  which  the  letters  represent  the  weights  of  the  correspond- 
ing elements  in  one  pound  of  the  fuel.  The  result  is  in 
B.  T.  U.  This  equation  gives  results  that  agree  very  well 
with  Mahler's  experimental  determinations,  as  shown  by  the 
table  on  page  52. 

For  example,  the  total  heat  of  combustion  of  Pittsburg 
bituminous  coal,  for  which  the  ultimate  analysis  in  the  table 
on  page  41  gives 

0  =  0.7647,      H  =  0.0519,      O—00810,.    N=  0.0145. 

appears  by  Dulong's  formula  to  be 

14650  C  +  62, 100  (H  -  \  O) 

-   .  ^     /        o.o8io\ 
=  14,650  X  0.7647  +  62, 100  (0.05  19 — \ 

=  13,720 B.  T.  U. 

Mahler's  formula  for  the  same  coal  gives 

14,650  c  +62, 100  H  -5400  (O'+N) 
=  14,650  X  0.7647  -\-  62, 100  X  0.05  19 

—  5400(0.0810-1-0.0145) 
=  13,9106.  T.  U. 

Air  required  for  Combustion. — If  the  moisture  and  car- 
bon dioxide  in   the  air  be  neglected,  and  if,  further,  the  argon 


FUELS  AND    COMBUSTION. 


59 


is  not  distinguished  from  the   nitrogen,  then  we  have  for  the 
composition  of  the  atmospheric  air, 

By  weight    \0xy%en °-232 

(  Nitrogen o.  768 

By  volume  {  ^en a2°94 

(  Nitrogen 0.7906 

For  rough  calculations  it  is  customary  to  consider  that  the 
atmosphere  is  made  up  of  one  volume  of  oxygen  and  four 
volumes  of  nitrogen.  This  approximation  is  sufficient  for 
calculation  of  air  required  by  fuels,  and  for  similar  purposes. 

The  air  required  for  combustion  of  a  given  fuel  may  be 
estimated  from  its  composition  and  from  the  composition  of 
the  air.      A  few  examples  will  make  the  process  clear. 

Thus,  carbon  burned  to  CO,  requires  two  portions  of 
oxygen,  so  that  one  pound  of  carbon  will  require 

2  X  16 

—  23 

12 

pounds  of  oxygen.      Since  air  is  0.232  part  oxygen  by  weight, 
one  pound  of  carbon  will  require 

2$-f-  0.232  =  11.5 

pounds  of  air  for  complete  combustion. 

In  like  manner  one  pound  of  hydrogen  will  require 

2 
pounds  of  oxygen,  or 

•  8  -T-  O.232  =  34.5 

pounds  of  air  for  complete  combustion. 

Another  method  of  calculation  is  based  on  the  approxi- 
mate composition  of  air,  i.e.,  one  volume  of  oxygen  and  four 
of    nitrogen.      This    method    depends    on    the    fact    that   the 


60  STEAM-BOILERS. 

weights  of  a  cubic  foot  of  different  kinds  of  gases  are  propor- 
tional to  their  atomic  weights  ;  so  that  if  the  weight  of  a  cubic 
foot  of  hydrogen  be  taken  for  the  basis  01  comparison  and  be 
called  unity,  then  the  weight  of  a  cubic  foot  of  oxygen  will 
be  i6,  while  that  of  nitrogen  will  be  14.  We  shall  then  have 
for  the  approximate  composition  of  air  one  volume  of  oxygen 
having  the  weight  16,  and  four  volumes  of  nitrogen  having  each 
the  weight  14.  In  order  to  get  one  pound  of  oxygen  we 
must  take 

(16  +  4  X  14)-^  16=  4i 

pounds  of  air. 

It  has  already  been  shown  that  one  pound  of  carbon  will 
require  2§  pounds  of  oxygen.  By  the  method  just  stated  it 
appears  that  a  pound  of  carbon  will  require 


>-' 


X  4i  =  12 


pounds   of  air.      This   result   is   often    quoted    and    is    easily 
remembered. 

Since  a  pound  of  hydrogen  requires  8  pounds  of  oxygen, 
this  method  gives 

3  X  4i  -  36 

pounds  of  air  for  each  pound  of  hydrogen. 

In  calculating  the  air  required  for  a  fuel  it  is  customary  to 
use  the  convention  proposed  by  Dulong  for  finding  heat  of 
combustion,  namely,  that  each  pound  of  oxygen  in  the  fuel 
renders  one  eighth  of  a  pound  of  hydrogen  inert,  and  that  the 
remainder  of  the  hydrogen  and  all  the  carbon  can  be  treated 
as  free  elements.  In  using  this  convention  it  is  customary  to 
take  the  approximate  weights  of  air  just  calculated  for  a 
pound  of  carbon  and  a  pound  of  hydrogen.  The  convention 
can  then  be  stated  in  the  form  of  an  equation  as  follows: 

Air  per  pound  ot  tuel  =  12  C  -j-  36  (H  —  \  O), 


FUELS   AND    COMBUSTION.  6 1 

In   which   the  letters  C,   H,  and   O   represent   the  weights   of 
carbon,  hydrogen,  and  oxygen  in  one  pound  of  the  fuel. 
An  application  of  this  equation  to  Pittsburg  coal  gives 

A-                            ^                ^/                      0.08  io\ 
Air  =  12  X  0.7647  -{-  36(0.0519 — •  I  =  10.7  pounds. 

This  result  is  somewhat  larger  than  would  be  obtained  were 
the  more  exact  composition  of  the  atmosphere  given  on  page 
59  used,  together  with  the  assumption  that  the  oxygen  ren- 
ders inert  its  equivalent  of  hydrogen  ;  but  the  method  is  not 
sufficiently  well  grounded  to  warrant  much  refinement. 

As  a  further  illustration  of  the  method  the  following  cal- 
culation of  the  air  required  for  one  pound  of  olefiant  gas  may 
be  interesting.  This  gas,  having  the  composition  CaH4,  con- 
sists of 

2  X  12  6 

—        — ■ =  —  carbon, 

2  X  12  +4  X  1        7 

=  -  hydrogen, 


2  X  12  +4  X  1        7 
and  will  require 

f  X  124-4x36=  1 5.4  pounds  of  air. 

Air  for  Dilution. — In  order  to  secure  complete  combustion 
of  coal  in  the  furnace  of  a  boiler  it  is  necessary  to  supply  an 
excess  of  oxygen,  or,  what  amounts  to  the  same  thing,  an 
excess  of  air.  This  excess  varies  from  one  half  the  quantity 
required  for  combustion  to  an  equal  quantity.  Thus,  roughly, 
from  18  to  24  pounds  of  air  may  be  furnished  per  pound  of  car- 
bon and  from  54  to  72  pounds  of  air  per  pound  of  hydrogen. 

Volume  of  Air  for  Combustion. — The  table  on  page  55 
gives  the  density  or  weight  of  one  cubic  foot  of  the  several 
gases  mentioned,  also  the  reciprocal  of  the  density  or  the 
volume  occupied  by  one  pound  of  the  gas.  This  is  called  the 
specific  volume  of  the  gas.  The  specific  volume  of  air  is 
12.39    at    the    pressure    of    the     atmosphere  and  at  the  temper- 


62  STEAM-BOILERS. 

ature  320  F.  The  volume  of  a  pound  of  gas  increases  as  the 
temperature  rises.  At  6o°  F.  one  pound  of  air  will  occupy 
about  13  cubic  feet.  To  find  the  volume  of  air  required  per 
pound  of  fuel  we  may  simply  multiply  the  weight  by  13,  for 
ordinary  calculations.  Thus  we  shall  have  for  the  air  per 
pound  of  the  principal  elements  in  fuels: 

Without  With  50  per        With  100  per 

Dilution.       cent  Dilution,     cent  Dilution. 

Carbon   150  225  300 

Hydrogen 45°  675  9°° 

These  approximate  values  are  sufficient  for  determining 
the  dimensions  of  doors  or  passages  through  which  air  is 
supplied  to  the  fire. 

This  method  applied  to  Pittsburg  coal  will  give,  approxi- 
mately, 

10.7  X  13  =  139 

cubic  feet  of  air  for  each  pound  of  coal  without  dilution. 
With  dilution  of  50  per  cent  the  air  required  will  be  about 
210  cubic  feet  for  each  pound. 

Sometimes,  in  connection  with  boiler-tests  or  for  other 
purposes,  a  more  exact  estimate  of  the  amount  of  air  is  de- 
sired. The  calculation  for  this  purpose  can  be  best  explained 
by  aid  of  an  example. 

Example. — Required  the  weight  and  volume  of  air  needed 
for  combustion  of  Pittsburg  coal  with  50  per  cent  dilu- 
tion, the  temperature  of  the  atmosphere  being  yo°  F.  and 
the  height  of  the  barometer  being  29  inches,  when  reduced 
to  320  F. 

This  coal  is  composed  of  76.47  per  cent  carbon,  5.19  per 
cent  hydrogen,  and  8.10  per  cent  oxygen.  Assuming  that 
the  oxygen  renders  inert  one  eighth  of  its  weight  of  hydrogen, 
there  will  be  available 

8.10 

5. 19 =  4. 18  per  cent 

o 


FUELS  AND    COMBUSTION.  03 

of  hydrogen  and  76.47  per  cent  of  carbon.  Since  one  pound 
of  carbon  requires  2§  pounds  of  oxygen,  and  one  pound  of 
hydrogen  requires  8  pounds,  the  weight  of  oxygen  required 
per  pound  of  coal  is 

2%  X  0.7647  +  8  X  0.0418  =  2.374  pounds. 

But  air  contains  23.2  per  cent  of  oxygen  by  weight,  so  that  the 
air  required  per  pound  of  coal  is 

2.374-^-0.232  =  10.2  pounds. 

The  specific  volume  of  air  is  12.39,  so  tna^  each  pound  of 
coal  will  require 

10.2  X   12.39  —  126 

cubic  feet  of  air  at  the  normal  pressure  of  the  atmosphere 
and  at  32  °  F. 

To  find  the  volume  of  air  required  at  the  actual  pressure 
of  the  atmosphere  and  the  actual  temperature,  we  have  the 
facts  that  the  volume  of  a  given  weight  of  air  is  inversely  pro- 
portional to  the  absolute  pressure  and  directly  proportional 
to  the  absolute  temperature.  Now  the  absolute  pressure  of 
the  atmosphere  is  29  inches  of  mercury  as  given  by  the 
barometer,  while  the  normal  pressure  is  29.92  inches  of  mer- 
cury. To  get  the  absolute  temperature  we  add  459.5  t0  the 
temperature  by  the  thermometer;  the  absolute  temperature  of 
320  F.  is  491.5,  and  that  of  700  F.  is  529.5.  Under  the  con- 
ditions of  the  problem  the  air  required  per  pound  of  fuel  will 
have  the  volume,  without  dilution,  of 

126X X =  140 

491.5     29.00 

cubic  feet.  With  50  per  cent  dilution  the  volume  will  be  210 
cubic  feet. 

Determination  of  Air  per  Pound  of  Coal. — The  amount 
of  air  supplied  per  pound  of  coal  may  be  determined  either  bv 


64  S  TEA  M-B01LERS. 

measuring  the  air  supplied  to  the  furnace  or  by  an  analysis  of 
the  products  of  combustion. 

For  the  first  method  the  following  arrangement  has  been 
used  in  boiler-tests  at  the  Massachusetts  Institute  of  Tech- 
nology: The  ash-pit  doors  are  removed  and  a  sheet-iron 
mouthpiece  is  fitted  over  the  opening  into  the  ash-pit.  The 
air  for  combustion  is  supplied  by  a  cylindrical  sheet-iron  con- 
duit leading  into  this  mouthpiece.  The  area  of  the  conduit 
should  be  at  least  equal  to  the  area  of  the  fire-door  or  fire- 
doors,  and  its  length  should  be  several  times  its  diameter. 
The  velocity  of  the  air  in  the  conduit  is  measured  by  an  ane- 
mometer, from  which  the  volume  of  air  is  readily  calculated, 
and  its  weight  determined  from  the  temperature  and  pressure  of 
the  atmosphere.  The  joint  between  the  mouthpiece  and  the 
furnace  front  must  be  luted  to  avoid  leakage,  and  leaks  or  ad- 
mission of  air  to  the  furnace  otherwise  than  through  the  sheet- 
iron  conduit  must  be  stopped  or  allowed  for  Anemometers, 
even  when  tested  and  rated,  are  liable  to  be  affected  by  errors 
of  two  per  cent  or  more.  They  are  commonly  tested  by 
swinging  them  on  a  revolving  arm  through  still  air — a  method 
that  is  proper  for  small  or  moderate  velocities,  but  difficult  to 
use,  and  is  vitiated  by  the  action  of  centrifugal  force  at  high 
speeds.  An  ideal  way  of  testing  an  anemometer  would  be  to 
find  its  reading  in  such  a  conduit  when  the  weight,  and  con- 
sequently the  velocity,  of  the  air  per  second  is  known.  The 
weight  may  be  determined  by  causing  the  supply  of  air  to 
flow  through  a  well-rounded  orifice,  to  which  calculations  by 
the  proper  thermodynamic  equations  may  be  applied.  This 
method  for  large  conduits  would  involve  the  use  of  a  very  large 
air-compressor,  which  makes  it  hardly  practicable. 

Orsat's  Gas  Apparatus. — This  apparatus,  which  is  well 
adapted  to  the  analysis  of  flue-gases,  determines  the  propor- 
tion by  volume  of  the  carbon  dioxide,  carbon  monoxide,  and 
oxygen  in  a  mixture  of  gases.  The  remainder  of  tne  flue- 
gases  is  commonly  assumed  to  be  nitrogen,   but   it  includes 


FUELS   AND    COMBUSTION.  65 

unburned  hydrocarbon,  if  there  be  any,  and  steam  or  vapor 
of  water.  In  Fig.  27,  A,  B,  and  fare  pipettes  containing, 
respectively,  solutions  of  caustic  potash  to  absorb  carbon  diox- 
ide, pyrogallic  acid  and  caustic  potash  to  absorb  oxygen,  and 
cuprous  chloride  in  hydrochloric  acid  to  absorb  carbon  mon- 
oxide. 

At  W is  a  three-way  cock  to  control  the  admission  of  gas 
to  the  apparatus;  at  D  is  a  graduated  burette  for  measuring 
the  volumes  of  gas,  and  at  P  is  a  pressure-bottle  connected 
with  D  by  a  rubber  tube  to  control  the  gases  to  be  analyzed. 
The   pressure-bottle  is  commonly  filled  with  water,  but  glyc- 


FlG.    XO. 


erine  or  some  other  fluid  may  be  used  when,  in  addition  to  the 
gases  named,  a  determination  of  the  moisture  or  steam  in  the 
flue-gases  is  made. 

The  several  pipettes  A,  B,  and  C  are  filled  to  the  marks  a, 
b,  and  c  with  the  proper  reagents,  by  aid  of  the  pressure-bottle 
P.      With  the  three-way  cock  W  open  to  the  atmosphere,  the 
pressure-bottle  P  is    raised  till  the  burette  D   is  filled  with 
water  to  the  mark  m\  communication  is  then  made  with  the 
flue,  and  by  lowering  the  pressure-bottle  the  burette  is  filled, 
with  the  gas  to  be  analyzed,   and   two   minutes    are  allowed- 
for  the  burette  to   drain.      The  pressure-bottle  is  now  raised/ 
till    the  water  in  the   burette   reaches  the   zero-mark  and   the 


66  STEAM-BOILERS. 

clamp  k  is  closed.  The  valve  W'\s  now  opened  momentarily 
to  the  atmosphere  to  relieve  the  pressure  in  the  burette.  Now 
open  the  clamp  k  and  bring  the  level  of  the  water  in  the  pres- 
sure-bottle to  the  level  of  the  water  in  the  burette,  and  take 
a  reading  of  the  volume  of  the  gas  to  be  analyzed  ;  all  readings 
of  volume  are  to  be  taken  in  a  similar  way.  Open  the  cock 
a  and  force  the  gas  into  the  pipette  A  by  raising  the  pressure- 
bottle,  so  that  the  water  in  the  burette  comes  to  the  mark  m. 
Allow  three  minutes  for  absorption  of  carbon  dioxide  by  the 
caustic  potash  in  A,  and  finally  bring  the  reagent  to  the  mark 
a  again.  In  this  last  operation,  brought  about  by  lowering 
the  pressure-bottle,  care  should  be  taken  not  to  suck  the 
caustic  reagent  into  the  stop-cock.  The  gas  is  again  measured 
in  the  burette  and  the  diminution  of  volume  is  recorded  as  the 
volume  of  carbon  dioxide  in  the  given  volume  of  gas.  In  like 
manner  the  gas  is  passed  into  the  pipette  B,  where  the  oxygen 
is  absorbed  by  the  pyrogallic  acid  and  caustic  potash  ;  but  as 
the  absorption  is  less  rapid  than  was  the  case  with  the  carbon 
dioxide,  more  time  must  be  allowed,  and  it  is  advisable  to 
pass  the  gas  back  and  forth,  in  and  out  of  the  pipette,  several 
times.  The  loss  of  volume  is  recorded  as  the  volume  of 
oxygen.  Finally,  the  gas  is  passed  into  the  pipette  C,  where 
the  carbon  monoxide  is  absorbed  by  cuprous  chloride  in  hydro- 
chloric acid. 

The  solutions  are  as  follows : 

A.  Caustic  potash,   I  part;    water,  2  parts. 

B.  Pyrogallic  acid,  i  gramme  to  25  c.c.  caustic  potash. 

C.  Saturated  solution  of  cuprous  chloride  in  hydrochloric 

acid  having  a  specific  gravity  of  1. 10. 

The  absorption  values  per  cubic  centimetre  of  the  reagents 
are — 

A    Caustic  potash  absorbs  40  c.c.  carbon  dioxide. 

B.  Pyrogallate  of  potassium  absorbs  22  c.c.  oxygen 

C.  Cuprous  chloride  absorbs  6  c.c.  carbon  monoxide. 


FUELS   AND    COMBUSTION.  6 J 

Samples  of  gas  for  analysis  by  Orsat's  apparatus  should  be 
taken  from  the  back  of  the  furnace,  from  the  uptake,  and  from 
the  chimney ;  the  difference  in  composition  of  gases  at  the 
several  points  will  give  the  basis  for  calculations  of  leakage. 

When  it  is  not  convenient  to  draw  gases  from  the  flue  di- 
rectly into  the  measuring  burette  of  the  apparatus,  samples  of 
gas  may  be  drawn  into  glass  bottles  with  rubber  stoppers,  from 
which  gas  can  be  supplied  to  the  burette. 

Calculation  from  a  Gas  Analysis. — The  calculation  of  the 
amount  of  air  supplied  per  pound  of  carbon  and  per  pound  of 
coal,  from  the  known  chemical  constituents  of  the  flue-gases, 
is  best  shown  by  an  example. 

Example. — Let  it  be  assumed  that  the  analysis  of  the  flue- 
gases  resulting  from  the  burning  of  Pittsburg  bituminous  coal 
gives  by  volume  13  per  cent  of  carbon  dioxide,  0.5  per  cent 
of  carbon  monoxide,  and  6  per  cent  of  oxygen.  It  is  con- 
venient to  treat  the  percentages  by  volume  as  the  number  of 
cubic  feet  of  the  several  gases  in  one  hundred  cubic  feet  of  flue- 
gas.      We  will  thus  have — 

Density. 
Gas.  Volume.    (See  page  55.)       Weight. 

Carbon  dioxide 13         0.12345      1.6043 

Carbon  monoxide 0. 5      0.07806     0.03903 

Oxygen 6         0.08928     0.53568 

Now  one  pound  of  carbon  dioxide  is  composed  of 

2  X   16  8 

12  -f-  2  X  16       11 

of  a  pound  of  oxygen  and  3/1 1  of  a  pound  of  carbon,  and  a 
pound  of  carbon  monoxide  is  composed  of 

16  4 

12  -f-  16  ~~  7 

of  a  pound  of  oxygen  and  3/7  of  a  pound  of  carbon.      Conse- 
quently we  have 


68  STEAM-BOILERS. 


T\  X    I.6043  =    I- 1668  y\    X    I.6043  =0.4375 

4  X  0.03903   =  0.0223      I  X  0.03903   =  0.0167 


0-5357 


Pounds  of  oxygen,  1.7248  Pounds  of  carbon,  0.4542 

And  as  air  consists  of  0.232  part  by  weight  of  oxygen,  the  air 
per  pound  of  carbon  from  the  gas  analysis  is 

1.7248  ,  , 

— i — _ — ■-  0.232  =  16.4  pounds. 

0.4542 

The  coal  in  question  contains  76.47  per  cent  of  carbon,  5. 19 
percent  of  hydrogen,  and  8. 10  percent  of  oxygen.  Of  these 
elements  Orsat's  apparatus  accounts  for  the  carbon  only;  the 
oxygen  and  hydrogen  together  with  unburned  volatile  matter 
pass  off  with  the  nitrogen. 

The  analysis  shows   16.4   pounds  of  air  for  each  pound  of 

carbon ;   consequently  the   carbon   in   one   pound   of  coal   will 

require 

0.7647  X   16.4  =  12.5 

pounds  of  air.  Assuming  that  the  oxygen  in  the  coal  renders 
one  eighth  of  its  weight  of  hydrogen  inert,  and  that  the  re- 
mainder will  require  36  pounds  of  air  per  pound  of  hydrogen, 
we  shall  have 


,/                    o.o8io\ 
36(0.0519 — )  =  1.5 


of  a   pound  of  air  required    for  the   hydrogen.      So  that  the 
total  air  per  pound  of  coal  is  about 

12.5  4-  1.5  =  14  pounds. 

The  calculation  just  given,  involving  the  use  of  the  densities 
of  the  several  gases,  is  perhaps  the  most  readily  understood  ; 
there  is  another  method,  which  gives  the  same  result  and  is 
more  expeditious,  depending  on  the  fact  that  the  weight  of  a 
gaseous  compound  referred  to  hydrogen  as  unity,  is  half  its 


FUELS   AND    C0MBUS1  IvK 


69 


molecular  weight.  This  quantity  is  called  the  vapor  density  of 
the  compound. 

Thus  the  vapor  density  of  carbon  dioxide,  C03 ,  is 

£(I2  +2    X    16)  =  22; 

and  the  vapor  density  of  carbon  monoxide,  CO,  is 

1(12  +  16)=  14. 

Assuming  as  before  that  in  each  100  cubic  feet  of  flue-gases 
there  are  13  cubic  feet  of  CO,,  0.5  of  CO  and  6.0  of  O,  we 
have  for  the  corresponding  weights,  based  upon  hydrogen  as 
unity, 

13    X22=  286  for  COa 

0.5  X  14  =      7  for  CO 

6.0  X  16=    96  for  O 

Total,         389 

The  last  result  depending  on  the  fact  already  noted,  that  the 
weights  of  elementary  gases  are  proportional  to  the  atomic 
weights. 

Now  each  pound  of  CO.,  contains  3/1 1  of  a  pound  of  carbon, 
and  each  pound  of  CO  contains  3/7  of  a  pound  of  carbon,  so 
that  of  the  286  parts  by  weight  of  CO,  we  shall  have 

T3T  X  286  =  78 

parts  of  carbon,  and  of  the  7  parts  by  weight  of  CO  we  shall 
have 

f  X  7  =  3 
parts  of  carbon.     The  total  weight  of  carbon  will  be 

78+3  =  81. 
The  weight  of  oxygen  is  clearly 

389  —  81  =  308. 


yo  STEAM-BOILERS. 

The  oxygen  per  pound  of  carbon  is  therefore 
308^81  =  3.80, 
and  the  air  per  pound  of  carbon  is 

^y--^  0.232  =  16.4 

pounds,  as  found  by  the  previous  calculation. 

Loss  from  Incomplete  Combustion. — The  presence  of 
even  a  small  amount  of  carbon  monoxide  in  flue-gases  is  evi- 
dence of  a  very  appreciable  loss  of  efficiency,  as  may  be  seen 
by  the  following  example,  quoted  from  a  test  made  on  a  32 5- 
horse-power  boiler  at  Lowell.  The  coal  used  was  George's 
Creek  Cumberland,  fired  by  hand. 

An  analysis  of  flue-gases  by  Orsat's  apparatus  showed  12.5 
per  cent  of  CO, ,  1.1  per  cent  of  CO,  and  4.1  per  cent  of  O, 
by  volume. 

Using  the  method  of  vapor  densities  for  making  the  calcu- 
lation, it  appears  that  the  C02  contained 

j3T  x  12.5  X'22  =  75  parts  of  carbon, 
and  the  CO  contained 

\  X  1.1  X  14  =  6.6  parts  of  carbon. 
Now  75  pounds  of  carbon  burned  to  C02  gives 
75  X  14.650  =  1,098,750  B.  T.  U., 
and  6.6  pounds  of  carbon  burned  to  CO  gives 
6.6  x  4400  =  29,040  B.  T.  U., 

or  a  total  for  all  the  carbon  of  1, 127,790  B.  T.  U. 

Had  all  the  carbon  been  burned  to  CO,,  the  heat  of  com 
bustion  would  have  been 

(75  +6.6)  14,650  =  1,195,440  B.  T.  U. 


FUELS  AND    COMBUSTION.  7 1 

The  loss  by  incomplete  combustion  was  consequently 
1,195,440  -  1,127,790 


1,195,440 


X  100  =  5.6  per  cent. 


The  actual  loss  may  be  placed  at  a  little  less  figure  than  5.6 
per  cent,  since  less  air  is  required  for  burning  carbon  to  CO 
than  for  CO,. 

Loss  from  Excess  of  Air. — The  ideal  condition  would  be 
to  supply  just  enough  air  to  burn  all  the  carbon  in  the  coal  to 
CO,  and  all  the  free  hydrogen  to  H,0  ;  it  is  necessary  to  use 
somewhat  more  air  than  required  for  complete  combustion  to 
avoid  the  formation  of  CO  and  the  attendant  loss  of  heat.  On 
the  other  hand,  too  great  an  excess  of  air  occasions  a  loss,  as 
that  excess  must  be  heated  to  the  temperature  in  the  chimney. 

As  an  example,  suppose  that  Pittsburg  coal  can  be  com- 
pletely burned  with  50  percent  excess  of  air,  but  that  100  per 
cent  excess  is  allowed  to  pass  through  the  grate. 

To  simplify  the  problem  we  will  neglect  the  effect  of  sul- 
phur and  of  the  ash,  more  especially  as  it  is  not  certain  what 
their  effect  is ;  we  know  only  that  it  cannot  be  very  impor- 
tant. 

Each  pound  of  carbon  will  yield  3§  pounds  of  CO,  and 
each  pound  of  hydrogen  will  yield  9  pounds  of  H,0.  There 
will  therefore  be 

3§  X  0.7647  =  2.8039  pounds  of  CO, ; 
9  X  0.0519  =  0.4671        "         "    H,0. 

In  the  calculation  for  the  weight  of  air  (page  63)  it  has 
been  shown  that  2.374  pounds  of  oxygen  and  10.2  pounds  of 
air  are  required  for  combustion.     There  is  therefore 

10.2  —  2.374  =  7.826 

pounds  of  nitrogen  in  the  air  for  combustion.  But  each 
pound  of  coal  contains  0.014  of  a  pound  of  nitrogen,  so  that 
the  total  nitrogen  is  7.840  pounds. 


72  STEAM-BOILERS. 

Now  the  heat  required  to  raise  the  temperature  of  one 
pound  of  a  substance  one  degree,  called  the  specific  heat,  is 
given  in  the  table  on  page  55.  For  carbon  dioxide  the  specific 
heat  is  0.2169,  and  the  heat  required  to  raise  2.8039  pounds 
one  degree  is 

2.8039  X  0.2169  =  0.6082  B.  T.  U. 

The  following  are  the  calculations  for  the  several  compo- 
nents of  the  products  of  combustion  : 

Weight.        s£ecitfic 

6  Heat. 

Carbon  dioxide,  C02. . .  .  2.8039  X  0.2  169  =  0.6082  B.  T.  U. 

Steam,  HaO. 0.4671  X  0.4805  =  0.2244       "■ 

Nitrogen 7.840    X  0.2438  =  1. 91 14       " 

Air  for  dilution  50$ 5.100    X  0.2375  =  1.2  112        " 

Total 3.9552        " 

If  the  external  air  is  at  6o°  F.,  and  the  gases  in  the  chim- 
ney are  at  5600  F.,  then  the  heat  in  the  chimney-gases  above 
the  temperature  of  the  air  is 

500  X  3.9552  =  1978  B.  T.  U. 

The  total  heat  of  combustion  of  this  coal  by  Dulong's 
formula  is  13800  B.  T.  U.  ;  of  this  about  10  per  cent  will  be 
lost  by  conduction  and  radiation.  There  will  then  remain  to 
be  transferred  to  the  water  in  the  boiler 

13800—  (1380+  1978)  =  10442  B.  T.  U. 

This  is  about  j6  per  cent  of  the  heat  generated  by  combus 
tion. 

Suppose  that  the  dilution  is  allowed  to  be  100  per  cent. 
so  that  5  additional  pounds  of  air  per  pound  of  coal  are  ad^ 
mitted  to  the  grate.      Then  to  the  above  total  must  be  added 


FUELS   AND    COMBUSTION.  73 

1.2112  B.  T.  U.,  making  in  all  5.1664  B.  T.  U.  Multiply- 
ing by  500,  the  difference  of  temperature  assumed 

500  X  5- 1664  =  2583  B.  T.  U. 

Assuming,  as  before,  10  per  cent  for  loss  by  radiation  and 
conduction  leaves 

13800  -  (1380  -f  2583)  =  9837  B.  T.  U. 

to  be  transferred  to  the  water  in  the  boiler.  This  is  about  72 
per  cent,  so  that  the  loss  by  the  excess  of  dilution  is  about  4 
per  cent. 

Hypothetical  Temperature  of  Combustion. — A  calcula- 
tion is  sometimes  made  of  the  temperature  of  the  fire  on  the 
assumption  that  the  total  heat  of  combustion  is  all  applied  to 
raising  the  temperature  of  the  products  of  combustion,  includ- 
ing the  ash.  In  the  case  of  Pittsburg  coal  it  has  been  found 
that  3-955-  B.  T.  U.  are  required  to  raise  the  products  of 
combustion  one  degree,  allowing  50  per  cent  for  dilution. 
This  coal  has  J.6  per  cent  ash,  for  which  a  specific  heat  of  0.2 
may  be  allowed.  We  must  therefore  add  to  the  total  just 
quoted 

.076  X  0.2  =  0.0152  B.  T.  U., 

making  in  all  3.9704  B.  T.  U.  Dividing  the  total  heat  by 
this  quantity,  we  get 

13800  -f-  3.9704  =  34800  F. 

for  the  elevation  of  temperature.  To  this  we  will  add  the 
temperature  of  the  air  admitted  to  the  furnace,  say  60°  F., 
making  35400  F.  for  the  hypothetical  temperature  of  the 
fire. 

Such  a  temperature  is  never  reached  in  the  furnace  of  a 
boiler,  for  the  combustion  is  not  instantaneous  and  is  not 
completed  in   the   furnace,  as  flames    commonly  extend   over 


74  STEAM-BOILERS. 

the  bridge-wall  or  into  the  combustion-chamber;  meanwhile 
there  is  an  energetic  radiation  from  the  glowing  fuel  and 
flame,  and  a  rapid  transfer  of  heat  from  the  hot  gases  to  the 
heating-surface  of  the  boiler.  The  better  the  fuel  and  the 
higher  the  hypothetical  temperature  of  the  fire  the  less  chance 
is  there  that  the  actual  temperature  will  approach  it. 

During  a  test  on  a  Babcock  &  Wilcox  boiler,  at  the 
Massachusetts  Institute  of  Technology,  it  was  found  that  the 
temperature  immediately  over  the  fire  was  about  iioo°F., 
while  the  temperature  in  the  chimney  was  4000  F. 

A  test  on  a  boiler  of  the  locomotive  type,  at  the  Boston 
Main  Drainage  Station,  gave  for  the  temperature  of  the  gases 
escaping  from  the  boiler  4390  F.,  while  the  steam  in  the 
boiler  was  about  337°  F.  The  gases  were  afterwards  reduced 
to  1 940  F.  by  passing  them  through  a  feed-water  heater. 
This  boiler  was  designed  for  and  gave  a  high  efficiency,  and 
the  results  obtained  may  be  considered  to  represent  first-rate 
practice. 

Volume  of  a  Ton  of  Coal. — 

Kind  of  Coal.  Cubic  Feel  to  Ton. 

Soft  coal 41  to  43 

Buckwheat  or  pea 37 

Nut 34 

Furnace  size 36 

Coke 76 


CHAPTER    IV. 
CORROSION   AND   INCRUSTATION. 

THE  water  supplied  to  a  boiler  for  forming  steam  may 
corrode  the  iron  of  the  boiler,  or  it  may  deposit  material  that 
can  form  a  scale  or  incrustation ;  both  actions  may  go  on  at 
the  same  time. 

Pure  water,  free  from  air  and  carbon  dioxide,  has  little  or 
no  solvent  action  on  iron,  even  though  some  other  metal, 
such  as  copper,  which  may  with  the  iron  form  the  elements  of 
a  galvanic  couple,  be  present.  On  the  other  hand,  iron  will 
not  rust  if  placed  in  an  atmosphere  of  dry  air  or  dry  carbon 
dioxide.  All  natural  water,  rain-water,  water  from  wells,  rivers, 
lakes,  or  the  sea,  contains  air  in  solution,  and  carbon  dioxide 
is  not  infrequently  found  in  such  waters.  Iron  is  rapidly 
acted  upon  by  water  containing  air  or  carbon  dioxide,  and,  on 
the  other  hand,  iron  rusts  rapidly  in  air  or  carbon  dioxide  when 
moisture  is  present.  Again,  distilled  water,  as  from  the  sur- 
face condenser  of  a  marine  engine  containing  more  or  less  oil, 
or  the  substances  resulting  from  the  action  of  steam  on  oil, 
causes  corrosion  in  boilers  that  are  free  from  scale.  To  avoid 
rusting  of  boilers  when  not  in  use  they  ought  to  be  either 
quite  dry  inside  or  they  ought  to  be  entirely  filled  with 
water — preferably  water  that  has  been  freed  from  air  by  boil- 
ing. In  the  American  Navy  it  has  been  the  custom  to  dry 
out  boilers  and  paint  them  inside  with  mineral  oil  preparatory 
to  laying  them  up.  In  the  English  Navy  the  boilers  are 
dried  out,  a  pan  of  glowing  charcoal  is  placed  in  the  boiler  to 

75 


76 


S  TEA  M- BOILERS. 


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CORROSION  AND    INCRUSTATION.  77 

consume  the  oxygen  of  the  air,  and  quicklime  is  introduced 
to  absorb  moisture. 

Mineral  Impurities. — The  impurities  found  in  water  sup- 
plied to  land  boilers  are  commonly  carbonate  of  lime  and 
sulphate  of  lime,  with  more  or  less  organic  matter,  and  some- 
times sand  or  clay  held  in  suspension.  The  table  on  page  76 
gives  the  number  of  grains  of  various  mineral  substances  held 
in  solution  in  water  from  several  sources. 

Water  supplied  to  land  boilers  is  either  hard  or  soft ;  the 
first  contains  appreciable  quantities  of  lime,  and  the  other 
usually  contains  little  solid  matter  of  any  sort.  The  first  three 
examples  in  the  table  on  the  preceding  page  may  be  taken  as 
typical  soft  waters,  and  all  the  others,  except  the  last  two,  as 
typical  hard  waters.  While  there  is  considerable  difference 
in  the  amounts  and  the  composition  of  the  solids  in  solution 
in  f.he  several  examples  of  hard  water,  it  will  be  seen  that 
they  are  all  characterized  by  a  considerable  amount  of  calcium 
and  magnesium  carbonates,  and  (with  the  exception  of  Nos.  6 
and  9)  accompanied  by  a  comparatively  small  amount  of  cal- 
cium and  magnesium  sulphates.  It  will  be  noticed  that  Mis- 
souri River  water  is  distinctly  worse  than  Mississippi  River 
water,  not  only  in  that  it  contains  more  of  the  carbonates, 
but  because  it  contains  a  considerable  quantity  of  sulphates. 
No.  9,  from  a  well  at  Downer's  Grove  on  the  C,  B.  and  Q. 
R.  R.,  a  few  miles  from  Chicago,  has  been  selected  as  an 
example  of  a  very  bad  hard  water,  especially  as  it  contains  so 
much  sulphate.  The  reason  for  considering  the  sulphates  of 
lime  and  magnesia  so  deleterious  will  appear  a  little  later. 
Note  will  be  made  that  the  water  from  the  Mississippi  River 
at  two  different  places,  and  presumably  at  different  seasons  of 
the  year,  vary  considerably,  especially  in  the  amount  of  mat- 
ter held  in  suspension. 

In  some  places  in  the  western  parts  of  the  United  States 
the  only  available  waters  for  making  steam  are  strongly  im- 
pregnated with    alkalies    and    borax.      Such   waters  have  so 


78  STEAM-BOILERS. 

deleterious  an  action  on  boilers  that  the  advisability  of  using 
a  surface  condenser,  as  at  sea,  the  distillation  of  water  by  a 
multiple-effect  evaporator,  or  the  introduction  of  a  supply  of 
good  water  even  from  remote  places,  is  worthy  of  considera- 
tion. If  the  use  of  such  water  cannot  be  avoided,  a  competent 
chemist  should  be  consulted  to  suggest  methods  for  ameliorat- 
ing the  bad  effects  so  far  as  possible.  As  each  case  is  liable 
to  require  special  treatment,  no  further  discussion  appears 
profitable  in  this  place. 

The  carbonates  of  lime  and  magnesia  are  held  in  solution 
in  water  by  an  excess  of  carbon  dioxide  and  are  completely 
precipitated  by  boiling.  They  are  thrown  down  from  water 
supplied  to  a  boiler,  in  the  form  of  a  white  or  grayish  mud, 
provided  there  are  not  other  impurities  that  cement  them  to 
gether  and  form  a  hard  scale.  The  customary  and  sufficient 
method  of  treating  boilers  supplied  with  water  containing  car- 
bonates of  lime  and  magnesia  is  to  let  the  boiler,  while  fulL 
cool  down,  and  then  run  out  the  water  and  thoroughly  wash 
out  the  boiler  with  a  strong  stream  from  a  hose.  If  the  water 
is  blown  out  under  steam-pressure  the  deposits  are  hardened 
and  are  removed  with  difficulty.  While  pure  carbonates  are 
easily  treated  as  just  described,  the  presence  of  other  impu- 
rities, such  as  oil  or  organic  matter,  or  of  sulphate  of  lime,  is 
likely  to  make  the  deposits  hard  and  adhering. 

Sulphate  of  lime  is  much  more  soluble  in  cold  than  in  hot 
water,  and  is  entirely  thrown  down  from  water  at  a  tempera- 
ture of  2800  F.,  corresponding  to  35  pounds  pressure  of  steam 
above  the  atmosphere.  It  forms  a  hard  and  adhering  scale, 
and  even  in  comparatively  small  quantities  has  a  bad  effect  on 
scales  and  deposits  composed  of  carbonates,  as  has  already 
been  suggested.  The  bad  effect  of  deposits  from  water  con- 
taining calcium  sulphate  is  much  ameliorated  by  introducing 
carbonate  of  soda  or  soda-ash  into  the  boiler  with  the  feed- 
water.  The  result  is  to  give  a  deposit  of  calcium  carbonate 
in  the  form  of  a  fine  white  powder,  which  must   be  washed 


CORROSION  AND    INCRUSTATION.  ]g 

or  swept  out,  and  sodium  sulphate  in  solution,  which  must  be 
blown  out  from  time  to  time. 

If  the  mineral  matters  in  the  water  are  known  from  a 
chemical  analysis,  the  quantity  of  carbonate  of  soda  to  be  used 
may  be  calculated  as  follows: 

Example. — Find  the  weight  of  carbonate  of  soda  required 
per  day  for  a  boiler  supplied  with  iooo  gallons  of  water  per 
day  from  the  well  at  Downer's  Grove. 

From  the  table  on  page  66  it  appears  that  each  gallon  of 
the  water  contains  14.037  grains  of  CaS04  and  25.422  grains 
of  MgS04.  The  formula  for  soda  crystals  being  NaaCOs  + 
ioHsO,  the  reactions,  neglecting  the  water  of  crystallization, 
will  be 

CaS04  +  NaaCO,  =  CaCO,  +  Na2S04 ; 
MgS04  -f-  Na2COa  =  MgCOs  +  Na9S04. 

If  x\  is  the  grains  of  carbonate  of  soda  to  act  on  the  cal- 
cium, we  have 

CaS04;Na,C03  +  ioH90  =  14.037  :  x, ; 
40-f-32  -f- 4  X  16  :  2  X  23  -f  12  +  3  X  164-  10(2  +  16) 

=  14.037:*,. 
.\  x1  =  29.52  grains. 

The  magnesium  sulphate  which  is  soluble  is  also  changed 
into  the  carbonate  and  thrown  down  as  a  white  precipitate, 
adding  to  the  deposit.  The  number  of  grains  of  carbonate 
of  soda  required  for  this  reaction  is  found  as  follows : 

MgS04:Na;iC03  +  ioH,0  =  25.422:*,; 
24+32+4X16:2  X  23  +  12  +  3X  16+  10(2+16) 
=  25.422  :  xt. 
.-.  x^=  60.59  grains. 

The  total  weight  of  carbonate  of  soda  per  gallon  is  therefore 
29.524-60.59=  90+, 


8o  5  TEA  M-BOIL  ERS. 

and  the  weight  required  for  iooo  gallons  is 

go  X  iooo 

=  12. o  pounds  per  day. 

7000 

It  is  advisable  that  soda,  or  any  other  chemical  for  acting 
on  the  impurities  of  feed-water,  shall  be  introduced  at  regular 
intervals.  Sometimes  a  weight,  or  measured  portion,  is  thrown 
into  the  feed-water  in  a  tank  or  reservoir,  from  which  it  is 
pumped.  Sometimes  the  chemical,  dissolved  in  water  or 
diluted  with  water,  is  placed  in  a  small  tank  or  receptacle  that 
may  be  temporarily  connected  with  the  suction  of  the  feed- 
pump. If  this  method  is  used  care  must  be  taken  not  to 
admit  air  to  the  pump  and  so  derange  its  action. 

Soda-ash  is  commonly  used  instead  of  carbonate  of  soda, 
as  it  is  cheaper  and  somewhat  more  efficient,  on  account  of  the 
caustic  soda  it  may  contain.  Its  chemical  composition  is 
uncertain,  and  it  is  therefore  impossible  to  make  satisfactory 
calculations  for  the  quantity  to  be  used.  This,  however,  is 
commonly  no  real  objection,  for  we  seldom  have  a  chemical 
analysis  of  the  water,  and  cannot  determine  directly  how  much 
soda  is  required. 

An  excess  of  soda  in  a  boiler  is  liable  to  cause  foaming, 
and  at  high  temperatures,  corresponding  to  pressures  now  ha- 
bitual for  steam-boilers,  the  soda  is  apt  to  attack  the  inside  of 
water-glasses ;  any  indication  of  either  action  should  raise  the 
question  whether  too  much  soda  is  used,  but  the  absence  of 
such  an  indication  does  not  show  that  we  are  using  the  right 
quantity.  When  a  hard  scale  is  formed  by  a  water  known  to 
contain  lime,  we  may  infer  that  sulphates  are  present,  and  may 
find  by  trial  the  amount  of  soda  to  be  used.  Unfortunately 
other  impurities,  such  as  organic  matter,  cause  the  formation 
of  hard  scale,  and  make  this  method  uncertain.  Such  impur- 
ities often  produce  discoloration,  and  thus  betray  their  pre3- 
ence.  The  deposits  of  lime,  whether  carbonates  or  sulphates, 
are  commonly  white  or  grayish,  or  sometimes  fawn  color. 


CORROSION   AND    INCRUSTATION.  8l 

It  is  sometimes  proposed  to  use  ammonium  chloride,  or 
sal-ammoniac,  to  break  up  lime  compounds;  in  the  first 
place,  only  the  carbonates  are  acted  upon  by  this  reagent, 
and  in  the  second  place,  the  reagent  itself,  or  the  resultant 
chlorides,  are  liable  to  be  broken  up,  giving  free  chlorine, 
which  attacks  the  boiler. 

Tannic  acid,  either  commercial  acid  or  in  the  crude  state, 
may  be  used  to  break  up  a  scale  already  formed  ;  but  as 
tannic  acid  does  not  decompose  the  sulphates  ,  and  as  the 
compound  of  the  acid  with  lime  is  not  soluble,  its  use  appears 
to  be  restricted.  Many  proprietary  boiler  compounds  depend 
on  tannic  acid  for  their  action.  Acetic  acid  may  also  be 
used  to  break  up  the  carbonates,  but  it  likewise  has  no  action 
on  the  sulphates;  the  carbonates  are  changed  into  soluble 
acetates,  and  can  be  blown  out.  Both  tannic  acid  and  acetic 
acid  attack  iron,  but  are  not  so  dangerous  as  sulphuric  or 
hydrochloric  acids,  which  are  sometimes  recommended  for 
breaking  up  scale.  When  a  scale  is  once  formed  the  safer 
way  is  to  remove  it  with  proper  chipping  and  scaling  tools; 
but  this  will  be  found  to  be  impossible  for  many  types  of 
boilers  unless  they  are  largely  dismembered  for  that  purpose. 

When  river-water  is  used  in  boilers,  various  earthy  im- 
purities are  liable  to  be  carried  into  boilers,  such  as  clay  and 
sand,  together  with  soluble  matters.  Even  waters  from 
ponds  or  wells  may  contain  considerable  matter  in  suspension. 
Such  substances  can  sometimes  be  removed  by  filtering  or  by 
allowing  the  water  to  stand  so  that  the  insoluble  matter  may 
be  deposited.  Very  commonly  a  systematic  blowing  out 
from  the  surface  of  the  water  and  the  bottom  of  the  boiler 
will  remove  such  impurities  from  the  boiler.  If,  however, 
lime  and  magnesium  carbonates  and  sulphates  are  present, 
suspended  matter  is  carried  into  the  scale,  and  the  scale  may 
be  made  more  troublesome  in  consequence.  The  carbonates 
are  more  likely  to  form  a  hard  scale  if  any  binding  material 
such  as  clay,  is  present. 


82 


S  TEA  M-fiOlLERS. 


Fig.  31  shows  the  section  of  a  feed-pipe  which  was  nearly 
choked  with  scale  from  lime-water.  Though  the  deposit  of 
scale  in  a  horizontal  piece  of  feed-pipe  where  the  water  may 
be  heated  by  conduction  and  otherwise,  especially  during 
intervals  of  feeding,  is  probably  more  rapid  than  in  the  boiler 
itself,  this  may  serve  to  call  attention  to  the  extent  to  which 
scaling  may  occur  when  precautions  are  not  taken. 


Fig.  31.* 

Lime-extracting  Feed-water  Heater.  —  It  has  been 
pointed  out  that  carbonate  of  lime  can  be  completely  pre- 
cipitated by  boiling  to  drive  off  the  excess  of  carbonic  acid  ; 
carbonate  of  magnesia  if  present  is  thrown  down  at  the  same 
time.  Also  sulphate  of  lime  is  thrown  down  at  2800  F.,  cor- 
responding to  35  pounds  pressure  above  the  atmosphere. 
It  is  evident  that  lime  compounds  can  be  removed  from  feed- 
water  by  heating  it  and  removing  the  precipitated  lime  before 
feeding  it  to  the  boiler.  For  this  purpose  we  may  use  a 
heater  such  as  the  Hoppes  heater  and  purifier  shown  by  Fig. 
32,  which  consists  essentially  of  a   series  of  cylindrical    pans 

*  This  figure  and  Figs.  35  to  38  were  kindly  loaned  by  the  Hartford  Steam 
Boiler  Inspection  and  Insurance  Co. 


COXKOSIOX   AND    IXCK  US  TA  TION. 


83 


of  sheet  steel,  1,  2,  3,  4,  5,  and  6.  The  feed-water  is  pumped 
into  the  upper  pan,  from  which  it  overflows,  and,  trickling 
along  the  bottom,  it  drops  into  the  pan  2.  From  2  the 
water  overflows  into  3,  and  so  on. 

The  capacity  of  the  heater  depends  on  the  number  of 
sets  of  pans,  which  varies  from  one  to  four.  The  pans  are 
enclosed  in  a  steel  shell,  from  which  one  end  may  be  removed 
for  cleaning  the  pans.  Feed-water  is  pumped  in  at  B\  steam 
from  the  boiler  is  admitted  at  A  ;  the  feed-water  after  being 
heated  and  purified   runs  out  at  D  on  the  way  to  the  boiler; 


Fig.  32. 

at   C  there  is  a  blow-out,  from  which  air  and  gases   may  be 
blown  out  when  the  heater  is  started,  or  at  other  times. 

It  is  desirable  that  the  pipe  D  shall  drop  down  below-  the 
water-level  in  the  boiler  before  any  turns  or  horizontal  pipes 
are  attached.  The  water  runs  from  the  heater  to  the  boiler 
by  gravity  only,  and  the  heater  must  be  placed  high  enough 
for  this  purpose.  It  is  also  desirable  that  the  feed-pump  be 
supplied  with  steam  from  the  heater  so  as  to  continually 
remove  the  carbonic  acid,  air,  or  other  gases  given  off  from 
the  feed-water. 


«4 


S  TEA  M-B01LERS. 


The  feed-water  as  it  trickles  along  the  under  sides  of  the 
pans  in  a  thin  film  is  heated  by  the  steam,  and  the  lime  com- 
pounds are  deposited  in  form  of  a  scale  or  incrustation, 
Meanwhile  mud,  sand,  and  other  mechanical  impurities  settle 
to  the  bottom  of  the  pans. 

After  the  heater  has  been  at  work  a  month  or  so,  depend- 
ing on  the  amount  of  lime  in  the  water,  the  pans  must  be 
removed  and  cleaned.  The  steam-pipe  and  the  pipe  leading 
to  the  boiler  are  shut  off  by  proper  valves,  and  cold  water  is" 
pumped  in  and  allowed  to  run  to  waste  at  the  blow-off.  The 
contraction  of  the  pans  cracks  off  hard  scale  and  makes  it 
easier  to  remove.  When  the  heater  is  first  opened  the  scale 
is  usually  soft  and  can  be  readily  removed;  it  is  liable  to 
harden  when  exposed  to  the  air  and  allowed  to  dry. 

A  heater  for  use  with  exhaust-steam,  by  the  same  makers, 
differs  from  this  mainly  in  that  there  is  a  device  for  extract- 
ing oil  from  the  steam  before  it  meets  the  feed-water,  and  in 
that  it  is  run  at  atmospheric  pressure.  .Such  a  heater  will  not 
remove  sulphate  of  lime ;  and  further,  since  it  is  difficult  if 
not  impossible  to  remove  oil  from  exhaust-steam,  it  is  proba- 
ble that  some  oil  will  be  carried  over  into  the  boiler. 

Sea-water. — The  following  table  gives  an  analysis  of  sea- 
water  by  Professor  Lewes  of  the  Royal  Naval  College,  to- 
gether with  an  analysis  by  him  of  a  typical  boiler  deposit  from 
a  marine  boiler: 

SALTS    IN    SEA-WATER    AND   COMPOSITION    OF    MARINE- 
BOILER   SCALE.* 


Calcium  carbonate  (chalk). . 
Calcium  sulphate  (gypsum). 

Magnesium  sulphate 

Magnesium  chloride 

Magnesium  hydrate 

Sodium  chloride  (salt) 

Silicia  (sandy  matter) 

Moisture. . 


Sea-water. 

Marine-boiler 

Grains  per  Im- 

Scale. 

perial  Gallon. 

Per  Cent. 

3-9 

O.97 

93-1 

85.53 

124.8 

220.5 

3-39 

1850.1 

2.79 

8.4 

I.I 

5-9 

*  Trans.  Inst.  Naval  Arch.,  vol.  xxx.  p.  330. 


CORROSION  AND    INCRUSTATION.  85 

The  three  principal  constituents  of  the  marine  scale  are  cal- 
cium sulphate,  calcium  carbonate,  and  magnesium  hydrate, 
of  which  the  first  forms  the  greater  part  of  the  scale. 

The  calcium  carbonate  is  kept  in  solution  by  the  carbonic 
acid  in  the  sea-water,  just  as  is  the  case  for  fresh  water  con- 
taining carbonate  of  lime,  and  is  deposited  when  the  carbonic 
acid  is  driven  off  by  heat.  There  is.  however,  a  reaction 
between  the  calcium  carbonate  and  magnesium  chloride  at  the 
temperature  and  pressure  in  the  boiler,  giving  a  deposit  of 
magnesium  hydrate  and  leaving  calcium  chloride  in  solution, 
so  that  only  part  of  the  calcium  carbonate  appears  in  the  scale  ; 
and  on  the  other  hand,  we  may  thus  account  for  the  presence 
of  the  magnesium  hydrate  in  the  scale. 

The  calcium  sulphate  forms  so  large  a  part  of  the  sca^e,  that 
vve  will  give  attention  to  it  only  in  the  further  discussion.  Cal- 
cium sulphate  is  more  soluble  in  water  at  95 °  F.  than  at  any 
temperature  higher  or  lower;  and  the  solubility  decreases  with 
the  rise  of  temperature,  till  at  about  2800  F.,  which  corre- 
sponds to  50  pounds  pressure  absolute  to  the  square  inch,  or 
35  pounds  above  the  atmosphere,  the  entire  amount  of  cal- 
cium sulphate  is  deposited.  In  the  early  history  of  the  marine 
engine,  when  low  pressures  of  steam  prevailed,  we  find  jet  con- 
densers in  use,  and  the  boilers,  which  were  fed  from  the  brine 
in  the  hot-well,  were  kept  fairly  free  from  scale  by  blowing 
out  the  concentrated  brine.  It  was  then  customary  to  supply 
half  again  as  much  feed-water  as  was  evaporated,  the  excess 
being  compensated  by  the  concentrated  brine  blown  out,  and 
the  water  in  the  boiler  had  three  times  the  degree  of  concen- 
tration found  in  the  sea.  As  high-pressure  steam  came  into 
use,  surface  condensers  became  indispensable.  When  surface 
condensers  first  came  into  use  the  waste  of  steam  from  leakage 
and  otherwise  was  made  up  from  water  taken  from  the  sea, 
with  the  result  that  the  boilers  gradually  accumulated  a  heavy, 
dense  scale.  Since  it  is  customary  to  have  an  auxiliary  boiler, 
called  a  donkey-boiler,  on  steamships,  the  first  device  to  avoid 
the  scaling  from  the  use  of  sea- water  in  the  main  boilers  appears 


86  S  TEA  M-BO ILERS. 

to  have  been  to  supply  the  loss  of  steam  from  the  donkey- 
boiler,  which  was  fed  from  the  sea.  This  of  course  only  trans- 
ferred the  difficulty  from  one  place  to  another,  even  though  a 
less  objectionable  one.  At  present  the  loss  is  made  up  by 
vaporizing  sea-water  in  a  special  boiler,  which  is  heated  by 
steam-coils  supplied  with  steam  from  the  main  boilers.  The 
pressure  may  be  low  enough  in  this  vaporizer  to  avoid  the 
total  precipitation  of  the  calcium  sulphate,  and  the  brine  may 
be  kept  at  any  desirable  degree  of  saturation  by  blowing  out, 
as  in  the  early  marine  practice  ;  and  further,  the  vaporizer  is 
so  made  that  the  steam-coils  may  be  readily  cleared  from 
scale. 

It  should  be  pointed  out  that  the  decomposition  of  the 
calcium  sulphate  in  sea-water  by  the  aid  of  soda  is  impracti- 
cable, on  account  of  the  large  quantity  of  magnesium  carbonate 
thrown  down  by  reaction  on  the  magnesium  sulphate. 

A  boiler  fed  with  water  condensed  in  a  surface  condenser, 
as  is  now  common  in  marine  practice,  is  liable  to  two  diffi- 
culties: (i)  the  distilled  water  is  apt  to  corrode  or  pit  the  plates 
of  the  boiler,  and  (2)  the  cylinder-oil  used  in  the  engine  is 
liable  to  be  carried  over  into  the  boiler  and  form  oily  scales 
and  deposits. 

When  sea-water  is  used  in  the  boiler,  either  as  the  main 
boiler-feed  or  merely  to  supply  the  waste,  the  boiler-plates  are 
protected  by  the  scale  of  calcium  sulphate,  and  general  corro- 
sion or  local  pitting  is  seldom  troublesome.  When  care  is 
taken  to  avoid  the  use  of  salt  water,  supplying  the  waste  with 
fresh  water  from  a  distiller  or  otherwise,  general  corrosion  and 
local  pitting  have  both  been  found  to  occur  to  a  dangerous 
degree.  A  simple  remedy  appears  to  be  to  form  a  very  thin 
scale  by  the  use  of  sea-water,  and  then  avoid  further  use  of 
sea-water.  It  is,  however,  found  that  water  from  a  surface 
condenser  will  gradually  dissolve  off  such  a  scale,  and  it  must 
be  occasionally  renewed.  There  is  also  an  objection  to  the 
introduction  of  any  lime  compound  into  a  boiler,  as  wili  appear 


COXAOS/OX    AXD    IXCRUSTAT10N.  gj 

in  the  discussion  of  the  difficult}-  from  the  collection  of  oil  in  the 
boiler.  In  both  the  United  States  and  the  English  navies  it  is 
customary  to  use  slabs  of  zinc  to  protect  the  boiler-plates  from 
corrosion.  The  zinc  is  fastened  to  or  hung  from  the  boiler- 
stays,  with  which  metallic  connection  should  be  made  to  in- 
sure galvanic  action.  The  zinc  is  gradually  consumed,  and 
becomes  soft  and  friable,  so  that  the  slabs  require  renewal. 
It  is  recommended  to  supply  1/4  of  a  pound  of  zinc  for  each 
square  foot  of  grate-surface. 

It  is  a  familiar  fact  that  the  cylinders  of  an  engine  may  be 
oiled  by  introducing  the  oil  into  the  supply-pipe,  and  that  the 
oil  will  be  carried  quite  thoroughly  over  the  surface  of  the 
cylinder  by  the  steam  ;  and,  further,  that  the  oil  is  carried  out 
of  the  cylinder  by  the  steam,  and  will  appear  in  the  condensed 
water  in  the  hot-well.  It  is  evident  that  any  oil  is  liable  to 
be  injurious  if  it  gets  into  a  boiler.  It  is,  consequently,  cus- 
tomary to  filter  the  water  from  a  surface-condenser,  to  remove 
the  oil  as  far  as  possible.  For  this  purpose  sponges  have 
been  used  in  the  navy ;  they,  of  course,  must  be  occasionally 
taken  out  and  washed  free  from  oil.  A  very  simple  and  effi- 
cient filter  has  been  made  in  the  form  of  a  rectangular  box, 
with  perforated  plates  near  the  ends;  the  water  from  the  hot- 
well  runs  into  one  end  compartment,  passes  through  a  mass  of 
hay  in  the  middle  compartment,  and  is  drawn  from  the  further 
end  compartment  by  the  feed-pump.  When  the  hay  becomes 
foul  it  is  thrown  away,  and  fresh  hay  is  put  in.  Professor 
Lewes  advises  for  a  filter  a  long  tube  filled  with  charcoal 
about  the  size  of  a  walnut ;  of  course  the  charcoal  should  be 
renewed  when  necessary.  It  cannot  be  expected  that  any 
system  of  filtering  will  remove  all  the  oil  from  the  water,  but 
the  larger  part  may  be  removed.  It  is  advisable  that  no  more 
oil  than  necessary  shall  be  used  in  the  cylinders  of  the  engine. 

Professor  Lewes*  gives  the  following  account  of  an  inves- 

*  Trans.  Inst.  Nav.  Arch.,  XXXII.  page  67. 


88  STEAM-BOILERS. 

ligation  of  the  collapse  of  the  furnace-flues  of  a  large  Atlantic 
steamer,  which  made  the  vcyage  in  twelve  days: 

The  boilers  were  five  and  a  half  years  old,  and  were  refilled 
with  fresh  water  at  the  end  of  each  voyage,  while  the  waste  of 
the  voyage  was  made  up  by  the  use  of  about  JO  tons  of  fresh 
water,  but  during  the  last  voyage  sea-water  was  used  for  this 
purpose.  Every  four  hours,  while  under  steam,  four  pounds 
of  soda  crystals  were  put  in  the  hot-well,  making  two  hundred- 
weight during  the  run,  the  total  capacity  of  the  boilers  being 
8 1  tons.  For  lubricating  purposes  seven  pints  of  valvoline 
were  used  in  the  cylinders  every  four  hours. 

When  in  port  the  boilers  were  allowed  to  cool  down,  and 
the  water  was  run  off  and  they  were  swept  down  with  stiff 
brushes,  and  were  afterwards  sluiced  out  with  a  hose  shortly 
before  being  filled  with  fresh  water.  No  trouble  occurred 
until  five  voyages  before  the  final  collapse,  when  some  of  the 
furnaces  began  to  creep  in  :  they  were  stiffened  with  rings  and 
stays;  and  on  succeeding  voyages  the  whole  of  the  furnaces 
got  out  of  shape  one  after  the  other.  Examination  showed 
that  they  had  never  been  very  heavily  scaled.  On  the  furnace- 
crow  n  there  was  only  a  slight  white  scale  not  more  than  1/64 
of  an  inch  thick,  while  on  the  bottom  of  the  furnaces  there  was 
a  brown  oily  deposit  1/16  of  an  inch  thick,  which  in  other 
parts  of  the  boiler  increased  to  1/8  or    3/16  of  an  inch. 

The  valvoline  was  a  pure  mineral  oil  with  a  specific  gravity 
of  0.889  ant^  a  boiling-point  of  37 1°  C. 

The  composition  of  scales  from  several  parts  of  the  boiler 
is  shown  in  the  table  on  the  next  page. 

Careful  examination  of  the  organic  matter  and  oil  in  these 
deposits  showed  that  half  of  it  was  valvoline  in  an  unchanged 
condition,  which  had  collected  around  small  particles  of  calcic 
sulphate. 

All  the  deposits  were  rich  in  oily  matter  except  the  top 
of  the  furnaces,  i.e.,  the  place  where  the  collapse  occurred. 
There  the  scale  was  not  only  nearly  free  from  oil,  but  per- 
fectly harmless   both   in   quantity  and  quality.      It   appeared 


CORROSION  AND    INCRUSTATION. 
COMPOSITION  OF  DEPOSITS  IN  A   MARINE  BOILER. 


o 

a  3 
-  u. 
•Z 

E  ti 

c  0 

—   X 

£  5 
c  — 

Si  ale  on  Tubes. 

I  >eposi(  above 
Scale  oil 
Tubes. 

Deposit  from 
Bottom  ol 

84-87 

5-9° 
2.83 

2-37 
3-23 
0  80 

59- '  1 
6.07 

1 1 .  2g 
2.85 

19  54 
1. 14 

t;o.i)2 

I  1- 

14.. 2 

7-47 
21.06 

1. 17 
1.08 

11.60 

0.82 

22.21 

9- 14 

50.20 

4  23 

1.S0 

22.52 

7.O9 
34.85 

27-95 

5-79 

i.8o 

Organic   matter  and   oil  ...  . 

Alkalies 

entirely  improbable  that  the  scale  on  the  top  of  the  furnaces 
could  be  in  its  original  condition. 

When  oil  has  entered  a  boiler  the  minute  globules,  if  in 
large  quantity,  coalesce  to  form  an  oily  scum  on  the  surface, 
or  if  in  small  quantity  remain  in  separate  drops,  but  show  no 
tendency  to  sink  on  account  of  their  low  specific  gravity. 
They,  however,  come  in  contact  with  solid  particles  of  calcium 
sulphate,  coat  them  with  oil,  and  so  the  light  oil  becomes 
loaded  till  it  is  easily  carried  along  by  convection-currents  and 
adheres  to  surfaces  with  which  it  comes  in  contact,  which 
are  quite  as  likely  to  be  the  under  •  surfaces  of  tubes  as  the 
upper  surfaces.  Since  some  brine  is  liable  to  find  its  way  to 
the  boiler,  from  leakage  into  the  condenser  or  otherwise,  even 
when  sea-water  is  not  used  directly,  this  action  will  occur  in 
a  boiler  supposed  to  contain  fresh  water  only. 

The  deposits  thus  formed  are  very  poor  conductors  of  heat, 
and  the  oily  surface  interferes  with  contact  with  water.  On 
the  crown  of  the  furnace  this  soon  leads  to  overheating  of  the 
plates,  and  the  deposit  begins  to  decompose,  the  lower  layer 
in  contact  with  the  plate  giving  off  gases  which  blow  up  the 
greasy  layer,  ordinarily  only  1/64  of  an  inch  thick,  to  a  spongy 
mass  1/8  of  an  inch  thick,  which,  because  of  its  porosity,  is  even 
a  better  non-conductor  of  heat  than  before,  and  the  plate  be- 
comes heated  to  redness  and  collapses.     During  the  last  stages 


9°  STEAM-BOILERS. 

of  this  overheating  the  temperature  has  risen  to  such  a  point 
that  the  organic  matter,  oil,  etc.,  in  the  deposit  burns  away, 
or  is  distilled  off,  leaving  behind,  as  an  apparently  harmless 
deposit,  the  solid  particles  round  which  it  had  originally  formed. 

Such  a  deposit  is  more  likely  to  be  produced  in  boilers 
containing  fresh  or  distilled  water,  as  the  low  density  of  the 
liquid  enables  the  oily  matter  to  settle  more  quickly,  while 
with  a  strongly  saline  solution  it  is  very  doubtful  if  this  sink- 
ing-point would  ever  be  reached;  it  is  evident  also  that  when 
oil  has  found  its  way  into  the  boiler  and  is  causing  a  greasy 
scum  on  the  surface  the  most  fatal  thing  that  can  be  done  is 
to  blow  off  the  boilers  without  first  using  the  scum-cocks,  be- 
cause as  the  water  sinks  the  scum  clings  to  the  tops  of  the  fur- 
naces and  other  surfaces  with  which  it  comes  in  contact,  and 
on  again  filling  up  with  fresh  water  it  still  remains  there, 
causing  rapid  collapse.  A  very  remarkable  instance  of  this 
is  to  be  found  in  the  case  of  a  large  vessel  in  the  Eastern  trade, 
in  the  boiler  of  which  an  oil-scum  had  formed.  The  ship 
having  to  stop  some  days  in  Gibraltar,  the  engineer  took  the 
opportunity  of  blowing  out  his  boiler  and  refilling  with  fresh 
water,  with  the  result  that  before  he  had  been  ten  hours  under 
steam  the  whole  of  the  furnaces  had  collapsed.  Under  some 
conditions  the  oil-coated  particles  coalesce  and  form  a  sort  of 
floating  pancake,  which,  sinking,  forms  a  patch  on  the  crown 
of  the  furnace  at  one  particular  spot,  and  under  these  condi- 
tions the  general  result  is  the  formation  of  a  pocket. 

A  curious  fact  is  that  these  oily  deposits  are  found  to  con- 
tain a  considerable  amount  of  copper.  Even  mineral  oils  have 
a  solvent  action  on  copper  and  its  alloys,  and  it  is  evident 
that  the  copper  in  the  oily  deposits  has  been  obtained  from 
the  fittings  of  the  cylinder  and  condenser.  Fortunately  this 
copoer  is  protected  by  oil,  otherwise  serious  galvanic  mischief 
would  result. 

Professor  Lewes  found  from  experiment  that  a  coating,  1/16 
of  an  inch  thick,  of  the  oily  deposit  found  in  the  bottom  of  a 


CORROSION   AND    INCRUSTATION. 


9* 


boiler,  applied  to  the  inside  of  a  clean  iron  vessel,  very  greatly 
retarded  the  transmission  of  heat  from  a  Bunsen  flame,  as 
shown  by  the  time  required  to  heat  a  known  quantity  of  water 
to  boiling-point.  Using  an  atmospheric  blowpipe,  he  succeeded 
in  raising  the  outside  surface  of  the  vessel,  when  coated  with 
1/16  of  an  inch  of  the  deposit,  to  the  temperature  of  the  melt- 
ing-point of  zinc,  and  with  an  oxy-coal-gas  flame  he  fused  a 
hole  in  the  bottom  of  a  thin  wrought-iron  vessel  thus  coated 
and  filled  with  water. 

He  further  says  that  cylinders  should  be  sparingly  lubri- 
cated with  a  pure  mineral  oil  having  a  high  boiling-point,  and 
that  animal  or  vegetable  oil  should  never  be  used,  because 
they  are  decomposed  by  the  action  of  high-pressure  steam, 
producing  fatty  acids  that  attack  iron,  copper,  and  copper 
alloys. 

Professor  Lewes  has  proposed  that  marine  boilers  at  sea 
shall  have  the  water  supplied  with  brine  from  which  the  lime 
compounds  have  been  precipitated  in  a  closed  receptacle  by  the 
combined  action  of  heat  and  carbonate  of  soda.  The  resulting 
brine  contains  mainly  sodium  and  magnesium  chlorides  and 
magnesium  sulphate,  which  do  not  form  scale  even  though  the 
concentration  is  carried  to  a  higher  degree  than  would  occur 
from  the  supply  of  the  waste  of  the  boiler  in  this  way  for  a 
voyage  of  some  length.  This  method  has  not  as  yet  been 
adopted  in  practice.  Attention  is  called  to  the  fact  that  an 
excess  of  soda  should  be  avoided,  since  it  would  cause  a  bulky 
deposit  from  the  action  on  the  magnesium  sulphate  brought  in 
by  leakage  of  sea-water  into  the  condenser.  A  description  of 
the  apparatus  for  producing  this  brine  without  lime  salts  is 
given  in  the  "  Transactions  of  the  Institution  of  Naval  Archi- 
tects" (see  the  leference,  page  84). 

Organic  Impurities. — Water  for  feeding  boilers,  unless 
taken  from  a  contaminated  source,  seldom  contains  much 
organic  matter.  Surface  water  from  rivers  or  ponds  may  con- 
tain some  vegetable  matter,  but  if  there  are  no  other  impun- 


02 


STEAM-BOILERS. 


ties  such  organic  matter  will  not  cause  much  trouble  unless  it 
is  allowed  to  accumulate.  The  vegetable  and  other  organic 
impurities  commonly  float  on  the  surface  of  the  water  when 
the  boiler  is  making  steam,  or  are  carried  around  by  convec- 
tion-currents, and  may  be  blown  out  through  a  surface  blow- 
out, shown  by  Fig.  33.      It  consists  essentially  of  a  flattened 


Fig.  33. 

bell  or  cone  of  sheet  metal  extending  across  the  boiler  at  the 
water-level,  and  turned  so  that  the  convection-currents  will 
carry  and  lodge  floating  substances  in  the  mouth  of  the  bell. 
The  valve  in  the  pipe  leading  from  this  bell  may  be  opened 
from  time  to  time  to  blow  out  the  substances  collected  in  it. 

When  a  boiler  has  been  at  rest  for  some  time,  overnight 
for  example,  the  various  solids  in  the  boiler,  if  heavy  enough, 
will  settle  to  the  bottom,  and  may  be  advantageously  blown 
out  before  starting  the  boiler  into  action  again.  This  may  be 
accomplished  by  opening  the  blow-out  valve  or  cock  for  a  short 
time,  until  the  water-level  falls  a  few  inches. 

Water  from  bogs  frequently  contains  vegetable  acids  that 
are   likely  to  corrode  the    plates   of  the  boiler:    in  such  cases 


CORROSION  AND    INCRUSTATION. 


93 


carbonate  of  soda  may  be   used  to  neutralize  the  acids;    the 
proper  amount  must  be  found  by  trial. 

The  oil  used  in  the  engine  is  liable  to  get  into  the  ooiier 
if  surface-condensing  is  made  use  of;  this  subject  has  already 
received  attention  in  connection  with  the  discussion  of  marine- 
boiler  incrustations.  Surface  condensers  are  not  commonly 
used  in  land  practice,  except  with  turbines.  The  exhaust-steam 
from  non-condensing  engines  is  used  for  heating  in  radiating- 
coilSj  and  there  is  an  apparent  gain  from  the  use  of  the  warm 


Fig. 


water  from  the  return-pipes.  This  water  is,  however,  liable 
to  be  contaminated  by  oil,  and  the  oil  when  it  gets  into  the  boiler 
may  cause  serious  damage,  such  as  was  found  to  occur  in  marine 
boilers.  If  the  feed  water  has  a  little  vegetable  matter  in  it,  the 
effect  of  the  oil  is  much  worse  than  if  the  water-supply  is  pure. 
Again,  the  oil  is  very  troublesome  if  the  water  contains  lime 
salts.  The  bad  effect  of  oil  or  other  impurities  on  lime-scale 
has  been  already '  noted.  Usually  it  will  be  found  better  to 
ieject  the  water  returned  from  a  heating  system  supplied  wi  h 
exhaust-steam,  as  the  apparent  economy  is  liable  to  be 
more    than    countei  balanced    bv    damage    to    the    boiler.      The 


94  5  TEA  M-B  OILERS. 

externally-fired  tubular  boilers  commonly  used  in  this  part  of 
the  country  are  liable  to  bulge  in  the  sheets  over  the  furnace, 
as  shown  in  Fig.  34,  if  oil  gets  into  them.  When  the  plate 
is  cut  out  a  hard  deposit  of  oil,  commonly  mixed  with  other 
impurities,  will  be  found  adhering  to  the  plate;  this  deposit 
is  a  very  poor  conductor  of  heat,  and  it  causes  so  much  over- 
heating of  the  plate  that  it  bulges  out  under  the  pressure  of 
the  steam. 

In  isolated  cases  it  will  be  found  that  water  of  a  stream 
may  be  so  contaminated  with  chemicals  from  some  industrial 
establishment  that  it  acts  energetically  on  the  boiler-plates; 
in  such  case  the  water  must  be  abandoned  unless  the  contam- 
ination can  be  stopped. 

Kerosene  and  Petroleum  Oils. — Both  crude  petroleum 
and  refined  kerosene  have  been  used  in  steam-boilers  to  miti- 
gate the  effect  of  incrustations  of  calcium  carbonate  and  calcium 
sulphate.  From  what  is  known  of  the  bad  effects  of  the 
heavier  petroleum  products,  such  as  the  mineral  oils  used  for 
lubricating  steam-engine  cylinders,  it  appears  to  be  unwise 
to  introduce  crude  petroleum  into  a  steam-boiler.  The  same 
objection  does  not  apply  to  refined  kerosene,  which  is  not 
known  to  have  any  bad  effect  in  a  boiler.  Both  oils  are  said 
to  change  the  deposits  of  lime  from  a  hard  scale  to  a  friable 
material,  which  may  be  easily  removed.  It  is  further  said  that 
these  oils  will  soften  and  loosen  scale  already  formed.  In  one 
case  40  gallons  of  kerosene  were  used  in  24  hours  in  the 
boilers  of  a  steamer  of  about  3000  horse-pow'er.  These 
boilers  showed  no  incrustation,  but  considerable  corrosion. 

Corrosion  is  distinguished  as  general  corrosion  or  wasting, 
pitting,  and  grooving. 

General  corrosion  is  difficult  to  detect,  as  it  acts  more  or 
less  uniformly  over  large  surfaces,  and  even  at  riveted  joints 
the  two  plates  and  the  rivet-heads  waste  away  equally,  so  that 
the  thinning  of  the  plates  is  not  easily  noticed.  Old  boilers 
not    infrequently   fail    from    general    corrosion,    and   then  are 


CORROSION  AND    INCRUSTATION.  95 

likely  to  fail  in  the  plate  rather  than  in  the  riveted  joint,  where 
the  double  thickness  of  plate  gives  an  advantage.  Boilers 
that  have  been  at  work  should  have  the  plates  below  the  water- 
line  drilled  and  the  thickness  measured;  if  the  effective  thick- 
ness of  the  plate  is  found  to  be  much  reduced,  the  working 
pressure   should    be    made    proportionately   lower.      Fig.     35 


Fig.  35- 

shows  an  example  of  general  corrosion,  and  Fig.  36  another, 
but  complicated  with  cracking  at  the  rivet -holes.  Both  show 
the  protection  given  to  the  plate  by  the  rivet-heads,  and  one 
may  readily  see  how  the  wasting  of  the  rivet-heads  may  be 
overlooked. 

Pitting  is  likely  to  occur  when  the  corrosion  takes  place 
rapidly.  It  appears  to  be  due  to  lack  of  homogeneity  of 
the  metal  of  the  plate,  and  sometimes  appears  to  indicate 
galvanic  action.  Though  every  precaution  to  avoid  gal- 
vanic action  should  be  taken,  it  is  better  to  assume  damage 
to  be  due  to  such  action  only  when  there  is  direct  evi- 
dence of  its  existence.  Fig.  37  shows  pitting  over  a  large 
surface,  and  Fig.  38  shows  local  pitting  in  the  corner  of  a 
flanged  plate  with  general  corrosion  of  the  flat  surface  of  the 
plate.  It  is  fair  to  assume  that  the  disturbance  of  the  metal 
in  the  process  of  flanging  may  determine  the  vertical  forms 
of  the  pitting.      The  horizontal  plate  shows  irregular  pitting. 

Grooving  is  usually  due  to  the  combination  of  springing 
or  buckling  of  a  plate  and  local  corrosion.  The  buckling  may 
be  due  to  insufficient  staying;  then  the  plate  springs  back 
and  forth  as  the  steam-pressure  varies.  Or  buckling  may  be 
due   to   improper   staying  or   fastenings,   which    localizes  the 


96 


S  TEA  M-BOILERS. 


Fig.  38. 


CORK OS 10 <N  AND    INCRUSTATION.  97 

change  of  shape  due  to  expansion.  In  either  case  the  metal 
is  fretted  at  the  place  where  the  greatest  bending  takes  place, 
and  very  much  weakened.  A  crack  is  liable  to  be  formed, 
which  may  grow  wider  and  deeper  till  the  plate  shows  signs 
of  failure.  Such  cracks  may  be  very  narrow  and  difficult  to 
find,  but  usually  the  fretting  of  the  metal,  whether  a  crack  is 
formed  or  not,  is  accompanied  by  local  corrosion,  which 
makes  a  groove  of  some  width.  If  the  water  used  forms  a 
scale  on  the  boiler-plates,  the  working  of  the  metal  throws 
off  the  scale  and  exposes  the  surface  to  the  water  so  that  cor- 
rosion takes  place  there,  though  elsewhere  the  plate  is  pro- 
tected. 

As  one  example  of  insufficient  staying,  we  may  take  the 
flattened  surface  in  a  wagon-top  locomotive-boiler  (Plate  II), 
where  the  barrel  is  expanded  to  join  the  shell  over  the  fire- 
box. The  surface  cannot  be  stayed  from  side  to  side  for  lack 
of  space  between  the  tubes,  and  is  merely  stiffened  by  rivet- 
ing three  pieces  of  T  iron  to  the  shell.  In  this  case  the  T 
irons  have  through-stays  at  their  upper  ends  over  the  tubes. 
Grooving  is  liable  to  occur  in  this  locality  even  when  the 
plates  are  stiffened  as  shown. 

Grooving  from  too  great  rigidity  is  liable  to  occur  in  the 
end-plates  of  Cornish  and  Lancashire  boilers  (see  pages  7  and 
8).  The  long  furnace-Hues  expand  more  than  the  external 
shell,  and  expand  more  at  the  top  than  at  the  bottom,  due  to 
the  heat  of  the  furnace  and  of  the  gases  in  the  flue  beyond 
the  furnace;  and  further,  the  circulation  of  water  under  the 
flues  is  likely  to  be  imperfect,  so  that  the  bottom  of  the  flue- 
is  not  so  hot  as  the  top.  These  unequal  expansions  must  be 
accommodate.!  by  the  springing  of  the  end-plates,  and  if  the 
springing  is  too  'much  localized,  grooving  is  sure  to  occur. 
The  kirnace-flues  should  be  at  least  nine  inches  from  the 
shell,  and  the  end-plates  should  be  flanged  where  the}-  are 
joined  to  the  flues  and  shell,  instead  of  using  angle-irons. 
The  use  of  gusset-plates  for  staving  the  ends  of  these  boilers 


98  STEAM-BOILERS. 

is  likely  to  give  too  much  rigidity  and  to  localize  the  spring- 
ing of  the  plates,  unless  care  is  taken  to  avoid  it. 

Grooving  from  either  too  great  or  too  little  rigidity  can  be 
avoided  only  by  a  proper  design,  which  must  be  guided  by 
experience.  If  a  boiler  shows  defects  of  staying,  it  may  be 
possible  to  put  in  additional  stays  after  the  boiler  is  com- 
pleted and  at  work;  or  in  some  cases  too  great  rigidity  may 
be  remedied  by  rearranging  the  staying.  Such  remodelling 
of  a  boiler  is  usually  difficult  and  unsatisfactory. 

Loss  from  Blowing  Out  Brine. — In  the  discussion  of 
the  use  of  sea-water  in  marine  boilers,  reference  was  made  to 
the  custom  of  feeding  one-and-a-half  times  as  much  water  as 
was  evaporated.  The  feed-water  was  taken  from  the  hot- 
well  of  the  jet  condenser,  and  was  nearly  as  salt  as  sea-water, 
which  contains  about  1/32  of  its  weight  of  salt.  The  one- 
half  excess  of  water  fed  was  blown  out,  and  carried  with  it  all 
the  salt  of  the  entire  feed-water;  it  consequently  contained 
3/32  of  its  weight  of  salt,  and  the  brine  in  the  boiler  had  the 
same  degree  of  concentration. 

In  calculating  the  loss  from  blowing  out  hot  brine  it  is 
customary  to  assume  that  the  specific  heat  of  sea-water  and 
also  of  the  hot  brine  is  the  same  as  that  of  fresh  water;  accu- 
racy in  this  calculation  is  not  essential. 

For  example,  find  the  loss  from  blowing  out  hot  brine  to 
maintain  the  concentration  in  the  boiler  at  3/32,  when  the 
boiler-pressure  is  30  pounds  by  the  gauge  and  the  temperature 
in  the  hot-well  is  1400  F. 

The  absolute  pressure  corresponding  to  30  pounds  by  the 
gauge  is  44. 7,  found  by  adding  the  pressure  of  the  atmosphere. 
Since  no  refinement  is  needed  in  this  calculation  we  will  use 
instead  45  pounds  absolute.  A  table  of  the  properties  of  satu- 
rated steam  (see  Appendix)  gives  for  the  heat  of  the  liquid  at 
45  pounds  absolute,  243.7  thermal  units;  this  is  the  heat  re- 
quired to  raise  one  pound  of  water  from  320  F.  to  274°.5  F., 
that  is,   to   the  temperature   of  steam   at  the  pressure  of  45 


CORROSION   AXD    INCRUSTATION.  99 

pounds.  The  same  table  gives  for  the  heat  required  to  vapor- 
ize one  pound  of  steam  from  water  at  2740. 5  against  a  pres- 
sure of  45  pounds,  927.5  thermal  units.  But  it  is  assumed  that 
the  feed-water  has  a  temperature  of  1400  F.  when  taken  from 
the  hot-well;  the  corresponding  heat  of  the  liquid  is  108.0 
thermal  units.  Consequently,  to  raise  a  pound  of  water  from 
1400  F.  and  vaporize  it  under  the  pressure  of  45  pounds  will 
require 

927.5  +  243.7  —  108.0  =  1063.2 

thermal  units.     This  is  the  heat  usefully  employed. 

Meanwhile  for  each  pound  of  water  vaporized  half  a  pound 
of  water  is  heated  from  1400  F.  to  274°.  5  F.,  and  then  thrown 
away.  The  heat  required  to  raise  half  a  pound  of  water  from 
1400  F.  to  2740. 5  F.  is 

1(2437  -  108.0)  =  67.8 

thermal   units.     This  is  the  heat  wasted. 

The  total  heat  applied  to  forming  steam  and  heating  the 
brine  blown  out  is 

1063.2  +  6~.S  —  1 1  31.0. 

The  per  cent  of  heat  wasted  is  consequently 

67S 

100  X  =  6  per  cent. 

1131.0 

A  considerable  portion  of  the  heat  lost  in  the  hot  brine 
may  be  transferred  to  the  feed-water  drawn  from  the  hot-well 
by  the  aid  of  a  feed-water  heater,  and  thus  saved.  A  simple 
form  of  heater  may  be  made  by  carrying  the  hot  brine 
through  a  small  pipe  inside  the  feed-pipe;  the  currents  of 
water  will  naturally  flow  in  opposite  directions,  and  thus  give 
the  most  efficient  interchange  of  heat.  If  the  hot-well  is  near 
fie  boiler,  the  feed-pipe  may  not  be  long  enough  to  allow  of 
this  form  of  heater. 


1 OO  S  TEA  M-BO ILEUS. 

The  density  of  brine  in  the  boiler  is  ascertained  by  a 
salimeter,  which  is  a  form  of  hydrometer  graduated  to  read 
zero  in  fresh  water,  1/32  in  sea-water,  and  the  graduation  is 
extended  to  give  the  density  of  brine  in  thirty  seconds,  so  far 
as  may  be  needed.  When  jet  condensers  were  used  at  sea  it 
was  customary  to  carry  the  density  to  3/32  only.  With  sur- 
face condensers  the  density  is  frequently  carried  as  high  as 
6/32  ;  no  inconvenience  is  found  in  this  custom,  and  as  less 
water  is  taken  from  the  sea  the  formation  of  incrustation  is 
less  rapid. 


CHAPTER   V. 
SETTINGS,   FURNACES.   AND   CHIMNEYS. 

The  Boiler-setting  for  a  stationary  boiler  consists  of  tne 
foundation  and  so  much  of  the  flues  and  furnace  as  are  ex- 
ternal to  the  boiler  proper.  The  entire  furnace  of  externally- 
fired  boilers  is  in  the  setting,  and  in  some  cases,  as  with  the 
plain  cylindrical  boiler,  the  flues  are  also  formed  by  the  set- 
ting. Some  internally-fired  boilers — for  example,  the  Lanca- 
shire boiler — have  flues  in  the  setting  in  addition  to  the  boiler- 
flues;  others,  like  the  upright  boiler  (Fig.  6.  page  n),  have 
only  a  foundation.  Locomotive-boilers  rest  on  the  frame  of 
the  locomotive ;  they  can  scarcely  be  considered  to  have  any 
setting.  Marine  boilers  are  seated  on  plates  that  are  built 
into  the  framing  of  the  ship. 

Foundations. — The  kind  of  foundation  needed  depends  upon 
the  type  of  boiler  to  be  set  and  upon  the  land.  With  boilers 
of  the  horizontal  multitubular  type  the  weight  is  distributed  by 
the  brickwork  of  the  side  walls  over  a  considerable  length  of  the 
foundation.  With  many  of  the  water-tube  boilers  the  load  is 
brought  to  the  four  corners  of  the  setting. 

On  good  land  a  floated  concrete  bed  2  feet  thick  extending 
1  foot  all  around  outside  of  the  setting  is  usually  sufficient. 

On  made  land,  piling  is  often  necessary.  The  piles  should 
be  cut  off  below  water  and  a  concrete  footing  made  over  the 
piles. 

The  safe  bearing  loads  carried  by  different  kinds  of  soil  are 
generally  taken  as  follows: 


102 


STEAM-BOILERS. 


Good  solid  natural  earth  4  tons  per  square  foot. 

Gravel,  well  packed  and  confined,  8  tons  per  square  foot. 

Dry  sand,  well  packed  and  confined,  4  tons  per  square  foot. 

Dry  sand  not  confined,  2  tons  per  square  foot. 

Marshy  soils  and  quicksands,  1/2  ton  per  square  foot. 

Soft  wet  clay,  1  ton  per  square  foot. 

Thick  beds  of  clay,  4  tons  per  square  foot. 


i ,  1 ;  i ;  1   g^ 

1  '  1  '  1  '  1      PT     FIRE  BRICK 


HARD  BRICK 


*£  '    'i' 1  i  t '  '  '  '     '  '  [...■■*  -^M  1  '  i  ' '  '  1 II ' ' 


Srt 


Fig.  39- 


Concrete  for  footings  may  be  mixed  in  the  following  pro- 
portions: Four  bags  of  Portland  cement,  three  barrows  or 
barrels  of  a  clean  sharp  sand,  and  five  barrows  of  crushed  stone. 
At  the  end  of  two  weeks  this  will  have  set  sufficiently  hard  for 
the  work  of  erecting  the  boiler  to  be  begun. 

Cylindrical  Tubular  Boiler-setting. — The  setting  for  a 
pair  of  cylindrical  tubular  boilers,  like  the  boiler  represented 
on  Plate  I,  is  shown  by  Figs.  39  and  40.  The  foundation  for 
the  boiler-setting  is  a  solid  bed  of  concrete  17  feet  8  inches  wide, 


SETTINGS,   FURNACES,   AND   CHIMNEYS. 


io3 


and  2i   feet  8  inches  long,  and  24  inches  thick.     On  firm  soil 
the  foundation  may  be  conveniently  made  of  large  rough-stone 


Fig.  40. 


work,  about  three  feet  wide,  under  the  side,  middle,  and  end 
walls  only. 


io4 


STEAM-BOILERS. 


On  this  foundation  there  are  built  the  walls  that  support 
and  enclose  the  boiler  and  the  furnace.  The  outer  walls  at 
the  sides  and  rear  are  double,  with  an  air-space  to  check  the 
conduction  of  heat.  The  boilers  are  each  supported  by  two 
brackets  at  each  end;  the  front  brackets  rest  on  iron  plates 
which  are  built  into  the  side  walls;  the  rear  brackets  have 
iron  rollers  interposed  to  allow  for  expansion.  A  brick, 
arch  is  sprung  over  the  boilers  to  check  the  radiation  of  heat. 
The  space  between  the  side  and  end  walls  over  the  boilers 
may  be  filled  with  sand,  for  the  same  purpose.  Coal  ashes 
are  sometimes  used,  but  they  are  hygroscopic  and  liable  to 
harbor  moisture  when  the  boilers  are  not  working,  and  should 
not  be  used.  Sometimes  the  tops  of  boilers  are  covered  with 
brick  and  buried  in  sand;  or  the  sand  may  be  used  without 
brick.  These  methods  give  ready  access  to  the  shell  for 
inspection  or  repairs,  but  are  not  so  good  as  a  brick  arch,  as 
water  can  more  readily  get  to  the  boiler  if  it  should  drip  from 
leaky  valves  or  fittings.  The  rear  wall  is  carried  a  little 
higher  than  the  top  row  of  fire-tubes,  then  the  space  is  bridged 
over  from  the  side  walls  by  a  horizontal  mass  of  brick- work, 
stiffened  and  supported  by  T  irons.  The  smoke-box  projects 
over  the  front  wall,  and  has  a  rectangular  uptake  on  top,  lead- 
ing to  a  wrought-iron  flue  which  carries  the  smoke  to  the 
chimney. 

The  furnaces  under  the  front  ends  of  the  boilers  arc 
enclosed  by  the  side  walls,  the  front  wall,  and  a  bridge  just 
beyond  the  first  ring  of  the  boiler-shell.  The  grates  rest  on 
the  front  wall  and  the  bridge,  as  shown  in  vertical  section  by 
Fig.  40  and  indicated  in  black  on  Fig.  39.  There  is  a  clear 
space  of  24  inches  between  the  grate  and  the  boiler,  and  a  clear 
space  of  8  inches  over  the  bridge.  The  top  of  the  bridge  is  made 
of  fire-brick,  and  all  the  walls  of  the  furnaces  and  other  spaces 
that  are  exposed  to  the  fire  are  lined  with  fire-brick.  The  fifth 
or  sixth  course  of  fire-brick  above  the  grate  should  be  laid  as 
headers,  which  serve  to  support  the  bricks  above,  while  the  brick 


SETTINGS,  FURNACES,   AND    CHIMNEYS.  105 

below  the  headers  are  being  renewed.  All  the  remainder  of  the 
brickwork  is  of  hard,  well-burned  brick.  The  ash-pit  under  the 
grate  is  paved  with  brick.  The  floor  behind  the  bridge  is  covered 
with  a  layer  of  sand  and  paved  with  brick. 

The  side  walls  are  braced  by  three  pairs  of  buck-slaves,  with 
through-rods  under  the  paving  and  over  the  tops  of  the  boilers. 

The  boiler  front  is  cast  iron,  with  doors  opening  from  the 
furnaces  and  from  the  ash-pits.  There  are  also  doors  opening 
from  the  smoke-boxes  to  give  access  to  the  tubes.  Doors  through 
the  rear  wall  give  access  to  the  space  behind  the  bridge-wall. 

Between  the  front  tube-sheet  and  wall  in  front  of  the  boiler 
there  should  be  a  distance  equal  to  the  length  of  a  tube;  for  it 
may  be  necessarv  in  a  few  months  to  replace  one  or  more  tubes. 
Sometimes  when  there  is  insufficient  room  the  boiler  is  placed 
opposite  a  door  or  a  window. 

The  tubes  are  cleaned  from  the  front,  that  is  to  say,  the  soot 
is  blown  from  the  inside  of  the  tubes  by  a  steam-jet  taken  in 
through  the  swinging-doors  of  the  front  covering  the  tubes. 

Any  number  of  boilers  of  this  type  can  be  set  side  by  side  in 
battery. 

If  it  is  desired  to  get  as  much  boiler  power  as  is  possible  in  a 
given  space,  using  this  type  of  boiler,  it  will  be  most  economical 
to  arrange  the  boilers  in  two  lines  with  the  fronts  facing  together 
with  a  distance  equal  to  the  length  of  a  tube  between  the  front 
tube-sheets. 

The  setting  for  a  two-flue  boiler,  or  for  a  boiler  with  several 
large  flues  in  place  of  the  numerous  fire-tubes  of  the  tubular 
boiler,  is  substantially  the  same  as  those  just  described. 

Babcock  and  Wilcox  Water-tube  Boiler  Setting. — 
This  boiler  is  suspended  from  a  framework  built  up  of  I-beams 
with  I-beam  columns  at  each  corner.  The  brickwork  carries  no 
load  whatever,  the  entire  load  coming  to  the  foundation  through 
the  columns. 

These  boilers  may  be  set  with  the  back  wall  against  the  back 
wall  of  the  boiler-house,  but  it  is  better  to  keep  at  least  3  feet 


io6  STEAM-BOILERS. 

between  the  two  and  to  bring  the  gases  out  through  an  opening 
in  the  back  wall  rather  than  to  take  the  gases  through  the  space 
between  the  two  drums. 

By  referring  to  Figs.  13  and  14  it  is  seen  that  in  order  to  blow 
the  soot  from  the  outside  of  the  tubes  three  openings  are  needed 
on  the  side  of  the  setting.  On  account  of  this  only  two  boilers 
can  be  set  together,  then  there  must  be  a  space  of  from  4  to  5 
feet. 

To  make  it  possible  to  renew  a  tube  in  the  boiler  there  should 
be  a  distance  between  the  bottom  hand-hole  in  the  header  and  the 
wall  equal  to  the  length  of  a  tube,  the  distance  being  measured 
in  a  line  parallel  with  the  tubes  in  the  boiler.  As  a  matter  of 
fact  the  hand-holes  being  elliptical  it  is  possible  to  get  a  tube 
in  even  if  this  distance  measures  3  or  4  inches  less  than  that  called 
for  by  the  above. 

Stirling  Water-tube  Boiler  Setting. — This  boiler  is  sus- 
pended in  practically  the  same  manner  as  the  Babcock  &  Wilcox. 
Its  tubes  are  cleaned  from  the  side,  and  access  to  the  drums  is 
from  the  side,  so  only  two  of  these  boilers  can  be  set  together. 

Heine  Water-tube  Boiler  Setting. — This  boiler  is  sup- 
ported at  the  bottom  of  the  water-legs.  The  front  water-leg 
rests  on  cast  iron  columns,  built  into  the  brickwork  and  tied 
together  by  the  casting  carrying  the  fire-  and  ash-pit  doors.  The 
rear  water-leg  is  supported  by  brickwork.  Between  the  brick- 
work and  the  water-leg,  plates  and  rollers  are  inserted  to  allow 
the  boiler  to  expand. 

The  tubes  in  this  boiler  are  cleaned  of  soot  by  blowing  jets 
of  steam  through  the  hollow  stays  which  tie  the  sides  of  the  water- 
legs  together. 

There  is  a  stay  in  the  center  of  the  space  between  four  tubes. 
The  tubes  are  blown  in  this  way  from  the  front  and  from  the 
back. 

Any  number  of  boilers  may  be  set  side  by  side,  but  there 
must  be  a  space  at  the  back  of  the  boiler-setting. 

The  hand-hole  covers,  covering  the  openings  opposite  a  tube, 


SETTINGS,  FURNACES,  AND    CHIMNEYS.  icy 

are  round  and  can  only  be  removed  by  dropping  them  down  to 
the  bottom  of  the  water-leg  where  a  larger  hole  is  left. 

Marine  Water-tube  Boiler  Settings. — Boilers  like  the 
Babcock  &  Wilcox,  Thornycroft,  Yarrow,  and  Almy  arc  en- 
closed in  a  sheet-iron  casing  lined  with  blocks  of  non-conducting 
material.  Asbestos,  or  a  compound  of  which  magnesia  is  a  prin- 
ciple ingredient,  is  commonly  used. 

Fire-brick  and  pumice-stone  are  used  with  the  Thornycroft 
boiler  to  intercept  heat  that  would  be  radiated  downward.  The 
spaces  in  ships  under  boilers,  being  more  or  less  inaccessible, 
and  being  subject  to  the  influence  of  heat  and  moisture,  are 
liable  to  show  excessive  corrosion. 

Furnaces. — There  are  certain  general  conditions  to  which 
the  construction  of  furnaces  should  conform  if  high  efficiency 
is  desired.  Some  of  these  depend  on  the  requirements  for 
good  combustion,  and  some  depend  on  the  size,  strength,  and 
endurance  of  the  human  frame,  since  hand-firing  is  almost 
universal.  Some  of  these  conditions  are  violated  in  the 
design  and  arrangement  of  furnaces  in  certain  types  of  boilers; 
deviation  from  them  involves  either  a  demand  for  greater 
strength  and  skill  on  the  part  of  the  fireman,  or  a  loss  of  effi- 
ciency, or  both. 

These  conditions,  with  examples  of  good  and  bad  practice, 
are  as  follows : 

There  should  be  an  abundant  and  uniform  supply  of  air  to 
the  under  surface  of  the  grate.  About  the  only  cases  where 
this  condition  is  not  easily  fulfilled  is  in  the  design  of  furnace- 
flues  of   Lancashire  boilers  and  Scotch  marine  boilers. 

A  small  supply  of  air  is  required  over  the  grate  for  burn- 
ing smoky  fuels  like  bituminous  coal.  This  air  is  very  com- 
monly supplied  through  a  circular  grid  or  damper  in  the  fire- 
door.  The  fire-door  is  commonly  protected  from  direct  radi. 
ation  by  a  perforated  wrought-iron  plate,  which  also  serves 
to  distribute  the  air  coming  through  this  grid.  Since  the 
air    thus  supplied    is   cold,    it  must    be    small    in    amount  or 


io8  STEAM-BOILERS. 

it  will  chill  the  gases  and  check  combustion  instead  of 
aiding  it. 

Leakage  of  cold  air  into  the  furnace,  or  into  the  combus- 
tion-chamber or  flues  beyond  the  furnace,  injures  the  draught 
and  reduces  the  temperature  of  the  products  of  combustion, 
and  is  a  direct  source  of  loss.  All  externally-fired  boilers  and 
water-tube  boilers  are  liable  to  suffer  from  leakage  of  air. 
Locomotive  and  Scotch  marine  boilers  are  usually  free  from 
this  defect. 

The  incandescent  fuel  on  the  grate  should  not  come  in 
contact  with  a  cold  surface.  Furnaces  lined  with  fire-brick, 
such  as  are  used  for  externally-fired  boilers,  conform  to  this 
requirement.  Vertical  boilers,  marine  boilers,  locomotive- 
boilers,  and  all  other  boilers  having  the  furnaces  in  fire-boxes 
or  flues,  violate  this  condition,  as  the  plates  in  contact  with  the 
fire  are  kept  nearly  at  the  temperature  of  the  water  in  contact 
with  the  other  side,  and  are  therefore  much  colder  than  the 
fire. 

There  should  be  an  abundant  opportunity  for  complete 
combustion  of  gases  coming  from  the  fuel  with  hot  air  drawn 
through  the  fuel,  before  the  flame  is  chilled  by  contact  with 
cold  surfaces.  This  condition  is  best  fulfilled  by  having  a 
clear  space  over  the  grate.  Externally-fired  boilers  commonly 
have  two  feet  or  more  between  the  grate  and  the  boiler-shell 
immediately  over  it,  and  combustion  may  continue  beyond 
the  bridge.  Locomotive- boilers  have  from  four  to  six  feet 
between  the  grate  and  the  fire-box  crown-sheet,  but  the  flame 
is  quickly  drawn  into  and  extinguished  by  the  tubes.  To  aid 
combustion  and  to  protect  the  lower  part  of  the  tube-sheet  a 
brick  arch  is  frequently  carried  across  the  fire-box,  over  which 
the  flame  must  pass  on  the  way  to  the  tubes.  The  lack  of 
space  over  the  grate  of  flue-furnaces,  as  in  the  Scotch  marine 
boilers,  is  only  partially  compensated  by  the  combustion- 
chamber  beyond  the  furnaces. 

Loss  from  external  radiation  is  almost  entirely  avoided   in 


SETTINGS,  FURNACES,  AXD  CHIMNEYS.  109 

internally- fired  boilers.  Externally-fired  boilers  are  subject 
to  more  or  less  loss  from  conduction  and  radiation. 

The  fire-grate  should  not  be  longer  nor  wider  than  can  be 
conveniently  reached  by  the  fireman  in  throwing  on  fuel  and 
in  cleaning  the  grate.  A  narrow  grate  should  not  be  so  long 
as  a  wide  grate.  In  general,  a  hand-fired  grate  should  not  be 
more  than  six  feet  long,  and  if  it  is  over  four  feet  wide  two 
fire-doors  should  be  provided.  These  conditions  are  usually 
fulfilled  by  the  design  of  externally-fired  boilers,  locomotive- 
boilers,  and  water-tube  boilers.  Attention  has  been  called 
already  to  the  difficulty  of  getting  proper  space  for  the  grates 
in  flue-furnaces.  With  the  common  diameters  of  the  furnace- 
flues  a  length  of  five  feet  should  not  be  exceeded.  Flues  in 
marine  boilers  have  been  made  eight  feet  long;  in  such  case 
the  further  end  of  the  grate  is  sure  to  be  inefficiently  fired. 
To  aid  in  firing,  and  to  use  the  space  below  and  above  the 
grate  to  the  best  advantage  for  the  supply  of  air  and  for 
combustion,  the  grate  is  commonly  given  an  inclination  down- 
wards of  about  3/4  of  an  inch  to  the  foot. 

As  an  extreme  example  of  deviation  from  these  propor- 
tions we  may  cite  the  Wooten  locomotive  fire-box,  designed 
to  burn  anthracite  slack.  The  grate  is  made  about  eight  feet 
wide  and  twelve  feet  long. 

For  convenience  in  throwing  on  coal  and  in  cleaning  the 
grates,  the  floor  on  which  the  fireman  stands  should  be  about 
two  feet  below  the  grate.  This  can  usually  be  arranged  for 
stationary  boilers.  The  grate  of  a  locomotive  is  commonly 
below  the  floor  of  the  cab ;  this  facilitates  throwing  on  the 
coal;  some  form  of  rocking  grate  is  used  to  shake  down  the 
ashes.  The  side  furnaces  of  Scotch  marine  boilers  are  com- 
monly too  high  for  convenient  firing,  and  the  middle  furnaces 
may  be  too  low  for  convenience  in  cleaning  the  grate. 

Excessive  heat  in  the  fire-room  should  be  avoided  as  far  as 
possible;  the  labor  of  feeding  and  cleaning  a  furnace  for  rapid 
combustion  is  always  severe,  and  when  combined  with  great 


I  TO  STEAM-BOILERS. 

heat  it  soon  exhausts  the  fireman.  If  land  boilers  are 
properly  clothed  to  avoid  radiation,  and  if  the  fire-room  is 
airy  and  well  ventilated,  the  heat  will  not  be  excessive.  It  is, 
however,  very  difficult  to  avoid  excessive  heat  in  the  stoke- 
hole of  a  steamship.  Of  course  the  radiation  from  the  glow- 
ing fuel  when  the  fire-doors  are  open  cannot  be  avoided,  but 
it  ought  to  be  possible  to  clothe  the  fronts  of  marine  boilers 
more  perfectly  than  is  now  the  common  practice.  Moreover, 
the  ventilation  of  the  stoke-hole  is  commonly  defective;  the 
air  pours  down  through  the  ventilators  and  makes  cold  spots 
immediately  beneath  them,  while  other  parts  of  the  stoke- 
hole are  hot.  Forced  draught  with  closed  stoke  hole  usually 
gives  good  ventilation ;  with  closed  ash-pit  it  is  liable  to  give 
defective  ventilation. 

In  certain  types  of  water-tube  boiler  there  is  not  sufficient 
space  over  the  fire  to  enable  the  gases  to  mix.  If  the  unmixed 
gases  are  chilled  by  coming  in  contact  with  the  cold  tubes  in- 
complete combustion  results.  Analyses  of  furnace-gas  samples 
taken  at  different  parts  of  the  gas  passage  often  show  CO  and 
an  excess  of  O.  This  shows  that  the  gases  were  not  mixed  till 
the  second  or  third  gas  passage  was  reached,  where  the  tem- 
perature was  too  low  for  the  CO  to  burn. 

The  Dutch  oven-furnace,  previously  referred  to  in  the  dis- 
cussion of  independently-fired  superheaters,  has  been  applied 
to  these  boilers  and  has  helped  somewhat.  By  raising  the  boiler 
up  and  using  the  Dutch  oven-furnace,  as  shown  by  Fig.  41,  the 
gases  mav  be  made  to  travel  9  or  10  feet  before  coming  in  con- 
tact with  the  tubes. 

This  setting  gives  very  nearly  complete  combustion  and  is 
very  efficient  as  a  smoke-consuming  device. 

A  relieving  arch  in  either  side  wall  carries  the  fire-bricks 
above  the  arch  and  makes  it  possible  to  renew  the  fire-brick 
adjacent  to  the  fire  without  disturbing  the  bricks  above. 

Great  care  should  be  taken  in  laying  the  fire-bricks  in  a 
furnace  of  this  sort.     The  bricks  should  be  laid  with  as  thin  a 


SETTINGS,    FURNACES,   AND    CHIMNEYS.  IXI 


1 1 2  STEA  M -BOILERS. 

layer  of  clay  between  them  as  will  serve  to  give  a  uniform  bear- 
ing. 

Fire-bricks  which  have  been  exposed  to  the  weather  during  a 
storm  or  fire-bricks  which  have  been  left  out  in  winter  weather, 
will  crumble  as  soon  as  they  are  heated  in  a  furnace. 

But  few  masons  seem  to  be  aware  of  this  fact. 

Grate-bars  are  commonly  made  of  cast  iron,  as  it  is 
cheaper  and  lasts  as  well  as  wrought  iron.  Sometimes  wrought- 
iron  bars  are  used  on  locomotives  and  elsewhere,  if  they  are 
expected  to  withstand  rough  usage. 

Cast-iron  fire-bars  are  generally  5  8  to  one  inch  thick  at  the 
top,  and  5/16  to  5/8  of  an  inch  thick  at  the  bottom;  they  are 
about  two  inches  deep  at  the  ends,  and  three  to  five  inches  deep 
at  the  middle.  To  provide  for  wasting  of  the  upper  surface, 
they  are  made  full  width  for  some  distance  down  from  the  top, 
thus  forming  a  sort  of  head;  then  they  are  rapidly  narrowed 
down  to  a  web  that  is  tapered  gradually  toward  the  bottom. 
The  space  between  the  bars  depends  on  the  draught  and  the 
nature  of  the  fuel;  with  ordinary  coal  and  natural  draught  3/8 
to  1/2  of  an  inch  is  allowed.  Lugs  or  projections  are  cast  at  the 
ends  and  at  the  middle,  so  that  the  bars  shall  be  properly  spaced 
when  laid  side  by  side.  With  forced  draught  the  bars  may  be 
3/8  to  9/16  of  an  inch  wide  at  the  top,  and  the  distance  between 
the  bars  may  be  1  16  to  1/4  of  an  inch.  The  area  of  the  air- 
spaces through  the  grate-bars  is  ordinarily  from  30  to  50  per 
cent  of  the  area  of  the  grate;  if  shavings  are  to  be  burned,  a  much 
greater  air-space  is  needed  and  a  grate,  like  Fig.  43,  is  often  used. 
The  combined  area  of  the  holes  may  be  made  as  great  as  the 
projected  area  of  the  bar,  thus  giving  100  per  cent  air-space. 
A  dead-plate  two  inches  wide  should  be  fitted  to  the  furnace- 
tube  of  marine  boilers  to  prevent  admission  of  air  at  that  place. 

The  length  of  fire-bars  should  not  exceed  four  feet;  the 
length  of  a  fire-grate  may  be  made  up  of  two  or  three  short  bars. 
Bars  are  commonly  cast  in  pairs,  or  three  or  four  may  be  cast 
together,  to  resist  twisting  and  warping  under  heat. 


SETTINGS,  FURNACES,   AND    CHIMNEYS. 


"3 


The  usual  form  of  grate-bar  cast  in  pairs  with  lugs  at  the  side 
is  shown  by  Fig.  42a. 

The  herring-bone  grate  is  shown  by  Fig.  42b;  a  grate  used 
for  sawdust,  shavings  or  other  inflammable  material  of  this  sort 


Fig.  42a. 


Fig.  42b. 

is  shown  by  Fig.  43.  Fig.  44  shows  a  form  of  grate  designed  by 
Prof.  Schwamb  for  burning  screenings  at  a  high  rate  of  com- 
bustion. The  construction  of  the  grate  is  shown  by  the  section. 
A  boss  around  each  air  opening  allows  ash  to  collect  in  the  small 


Fig.  43- 


recesses  between  the  air  openings  on  the  top  of  the  grate.  This 
ash  prevents  clinkers  from  adhering  to  the  bars.  Bars  of  this 
sort  have  been  used  twenty-four  hours  a  day  for  over  two  vears 
under  boilers  forced  80  per  cent  over  rating  without  trouble. 

Wrought-iron  fire-bars  are  formed  with  a  head  and  web, 
but  are  of  uniform  depth,  as  they  are  cut  from  a  rolled  bar;  thev 
are  bolted  together  in  ^ets  of  six,  with  washers  to  give  the  proper 


ii4 


STEAM-BOILERS. 


spacing.     For  marine  boilers  they  may  be  5/16  of  an  inch  thick 
at  the  top,  with  spaces  3/16  of  an  inch  wide,  or  less. 


Fig.  44. 

Rocking  Grates. — The  labor  of  breaking  up  the  clinker 
which  forms  on  grate-bars  is  very  much  reduced  by  employing 
some  form  of  rocking  grate.  On  locomotives,  where  the  rate  of 
combustion  is  hi^h  and  where  the  fire  should  always  be  in  good 
condition,  some  form  of  rocking  grate  is  considered  essential 
in  American  practice. 

In  Fig.  45  A  and  B  represent  alternate  grate-bars  which 
are  supported   at   semicircular  notches  at  the  ends.     CO   is  a 


a  b  a  b'  a" 


$7 


Fig.  45. 


cast-iron  crank-shaft  extending  across  the  furnace  at  one 
end  of  the  grate-bars.  Shallow  bars  like  A  rest  on  cranks 
that   are   above   the  line   CC,   and   deep  bars  like   B  rest   on 


SETTINGS,  FURNACES,  AXD  CHIMNEYS.  I  i  $ 

cranks  below  that  line,  as  shown  at  a,  a' ,  and  a",  and  at  b 
and  b' .  The  further  ends  of  the  grate-bars  rest  on  another 
crank-shaft  like  CC '.  At  the  lower  right-hand  corner  of  the 
figure  c"  represents  the  end  of  the  crank-shaft  and  d  repre- 
sents an  upper  crank  carrying  a  shallow  bar  like  A.  At  g  is 
a  head  to  which  a  lever  may  be  applied  to  rock  the  crank- 
shaft. When  the  crank-shaft  is  rocked  the  alternate  bars  are 
thrown  back  and  forth,  and  grind  up  the  clinker  so  that  it 
falls  through  the  grate  into  the  ash-pit. 

Firing. — Care,  skill,  and  intelligence  are  required  to  burn 
coal  rapidly  and  economically.  There  is  a  marked  difference 
in  the  ability  of  trained  firemen  to  make  steam  with  a  given 
boiler,  and  probably  there  is  nothing  more  wasteful  and  costly 
than  a  poor  or  careless  fireman. 

The  method  to  be  adopted  in  firing  depends  on  the  type 
of  boiler,  the  kind  of  coal,  and  the  rate  of  combustion.  Three 
methods  of  firing  may  be  distinguished : 

Spreadi)ig,  which  consists  in  distributing  small  charges  of 
coal  evenly  over  the  surface  of  the  fire  at  short  intervals.  In 
this  method  the  object  is  to  deliver  the  coal  just  where  it  is 
wanted,  and  then  not  disturb  it.  The  fire  can  then  be  kept 
in  just  the  right  condition  at  all  times,  and  probably  the  best 
results  can  be  thus  obtained,  both  in  absolute  quantity  of 
steam  and  in  economy,  provided  the  coal  used  is  well  adapted 
to  this  method.  Care  must  be  taken  to  have  the  door  open 
as  little  as  possible,  or  an  undue  amount  of  cold  air  will  be 
admitted  through  the  fire-door. 

Anthracite  coal  should  always  be  fired  by  spreading,  and 
should  be  disturbed  as  little  as  possible  after  it  is  thrown  in 
place.  Unless  the  fire  is  urged,  very  little  clinker  will  be 
formed,  and  the'  ashes  are  readily  shaken  out  by  a  pick  or 
hook  run  up  between  the  fire-bars.  The  thickness  of  the  fire 
may  vary  from  four  to  twelve  inches,  depending  on  the  size  of 
the  coal  and  the  strength  of  the  fire. 

Dry  bituminous   coal,  and   other  bituminous  coals,  if  not 


1 1 6  STEA  M -BOILERS. 

very  smoky  and  if  in  small  pieces,  can  be  advantageously  fired 
in  this  way.  Each  shovelful  thrown  on  will  give  off  volatile 
matter,  which  will  burn  with  the  excess  of  air  coming  through 
the  fuel,  and  very  little  smoke  will  result. 

Side  firing  consists  in  covering  all  of  one  side  of  the  fire 
with  fresh  fuel,  leaving  the  other  bright.  The  smoke  given 
off  from  the  fresh  fuel  can  then  be  burned  with  the  hot  air 
coming  through  the  bright  fire.  This  method  of  firing  is  best 
carried  on  with  two  furnaces  leading  to  a  common  combus- 
tion-chamber; the  furnaces  are  fired  alternately,  at  regular 
intervals,  with  moderate  charges  of  coal.  It  is  customary  to 
admit  air  through  the  grid  in  the  fire-door  when  the  fuel  is 
giving  off  gas. 

Coking  the  coal  on  a  dead-plate,  or  on  the  grate  just  inside 
the  fire-door,  is  perhaps  the  best  way  of  burning  a  smoky 
coal.  The  volatile  products  driven  off  from  the  heap  of  coal 
near  the  furnace-door  burn  with  the  hot  air,  coming  through 
the  clear  fire  at  the  rear.  As  soon  as  the  charge  is  coked  it 
is  pushed  back  and  spread  over  the  grate,  and  a  new  charge 
is  thrown  on. 

With  bituminous  coal  the  fire  should  be  thicker  than  with 
anthracite  coal:    from  6  to  16  inches  gives  good  results. 

The  method  too  often  followed  by  ignorant  and  indolent 
firemen,  of  throwing  on  as  much  coal  as  the  furnace  will  hold 
and  then  sitting  down  to  wait  till  the  steam-pressure  falls, 
needs  to  be  mentioned  only  to  condemn  it. 

Mechanical  Stokers,  feeding  coal  regularly  from  a 
hopper,  have  been  invented  in  a  variety  of  forms  from  time 
to  time.  Since  the  hopper  may  be  made  of  considerable 
size,  manual  handling  of  the  coal  may  be  entirely  avoided, 
and  one  man  can  easily  attend  to  a  number  of  furnaces  with 
little  labor  and  exposure  to  heat.  It  would  appear  also  that 
a  more  even  and  better  regulated  combustion  may  be  had 
than  with  hand-firing.  The  primary  object,  however,  is  to  save 
labor  and  it  is  foolish  to  install  a  mechanical  stoker  in  a  plant, 


SETTINGS,  FURNACES,  AND    CHIMNEYS.  117 

unless  a  saving  can  be  made  in  the  cost  of  labor  or  the  capacity 
of  the  plant  increased.  There  are  many  plants  equipped  with 
mechanical  stokers  where  the  hoppers  are  filled  by  the  shovel. 
Often  it  is  harder  to  shovel  the  coal  into  the-  hoppers  of  the  stoker 
than  it  would  be  to  throw  the  coal  on  to  the  grate,  and  as  many 
firemen  are  needed  as  would  be  required  to  lire  the  boiler  by 
hand. 

With  some  mechanical  stokers  working  under  forced  draught 
the  capacity  of  the  plant  may  be  increased  considerably  above 
what  could  be  obtained  by  hand  firing,  but.  in  general,  it  does 
not  pay  to  use  stokers  in  plants  of  less  than  1500  boiler  horse- 
power, as  the  saving  in  labor  is  not  great  enough  to  pay  for  the 
necessary  repairs  and  the  interest  on  the  first  cost  of  the  stokers. 

The  Roney  Stoker. — The  Roney  stoker,  shown  by  Fig.  46, 
as  applied  to  a  B.  &  W.  water-tube  boiler,  may  be  taken  as  an 
illustration  of  a  mechanical  stoker.  The  grate-bars  extend  across 
the  furnace  and  form  a  series  of  steps  down  which  the  fuel  slides, 
burning  on  the  way  down.  Each  grate-bar  is  hung  on  pivots 
at  the  ends,  near  the  top,  and  has  a  rounded  lug  at  the  bottom 
that  rests  in  a  groove  in  a  rocker-bar,  as  shown  by  Fig.  47. 

The  rocker-bar  has  a  slow  and  regular  reciprocation  de- 
rived from  a  small  steam-engine,  which  tips  the  grate-bars  so 
that  the  upper  surfaces  are  inclined  downward  to  make  the 
fuel  slide,  and  then  rights  them  to  check  the  motion  of  the 
fuel.  The  coal  from  the  hopper  falls  onto  a  horizontal  plate, 
from  which  it  is  pushed  forward  by  a  "  pusher  "  that  is  driven 
by  the  steam-engine  which  drives  the  rocker-bar.  The  rate 
of  feeding  the  fuel  can  be  controlled  by  changing  the  stroke 
of  the  pusher,  and  by  regulating  the  number  of  strokes  of  the 
pusher  and  of  the  rocker-bar  per  minute.  The  ashes,  clinker, 
and  other  unburned  refuse  collect  on  a  dumping-grate  at  the 
foot  of  the  grate-bars.  This  grate  is  shown  in  normal  position 
by  heavy  lines  in  Fig.  47,  and  in  the  dumping  position  by 
light  lines. 

This  grate  appears  to  be  well  adapted  to  burn  smoky  fuel, 


n8 


STEAM-BOILERS. 


Flow-  Line 


Pit  Fluor  LineV. 


Fig.  46 


SETTINGS,  FURN. I CES,  A  XD    CHIMNE VS.  \ ig 

as  such  fuel  is  well  coked  at  the  top  of  the  grate,  and  the  volatile 
parts  driven  off  by  coking  can  burn  with  the  excess  of  air  coming 
through  the  grate  at  the  bottom. 

If  tile  rate  of  feed  is  too  fast,  it  is  evident  that  unburned 
coal  will  work  down  onto  the  dumping- grate,  and  will  appear 
in  the  ashes.  If  the  rate  of  fuel  is  regulated  so  thai  no  coal 
appears  in  the  ashes,  the  fire  becomes  thin  at  the  bottom,  and 
an  excess  of  air  is  liable  to  enter  there;  certain  tests  on  this 
grate  have  indicated  such  an  excess  of  air,  which  is  the  side 
on  which  the  fireman  is  liable  to  err,  as  he  may  not  know 
how  much  waste  he  thus  occasions,  while  he  can  see  the  coal 
in  the  ashes. 

The  American  Stoker. — This  stoker  applied  to  a  hori- 
zontal multitubular  boiler  is  shown  by  Fig.  48.  The  grate  ordi- 
narily used  with  the  boiler  is  replaced  by  a  shallow  iron  trough, 
extending  nearly  to  the  bridge-wall.  The  trough  is  not  over 
one  third  of  the  width  of  the  regular  grate.  Fire-brick  are  laid 
either  side  of  the  trough,  thus  blocking  off  the  grate.  Air  from 
a  blower  is  sent  into  the  furnace  through  tuyer-blocks  located 
near  the  top  of  the  trough. 

The  jets  of  air  issuing  from  these  openings  are  inclined  up- 
wards by  a  trifling  amount. 

Coal  is  fed  from  the  hopper  to  a  worm  rotated  at  a  very  slow 
speed  by  a  steam  cylinder. 

The  coal  pushed  along  by  the  worm  rises  through  the  trough 
and  makes  a  mound  which  gradually  extends  on  to  the  brick 
cither  side  of  the  trough. 

The  fire  is  hottest  at  the  surface  of  the  mound  opposite  the 
tuyers.  Any  carbon  or  volatile  gases  driven  off  from  the  green 
coal  as  it  rises  through  the  trough  are  completely  consumed  in 
their  passage  through  the  hot  outer  layers. 

Both  this  stoker  and  the  one  shown  by  Fig.  49  increase  the 
capacity  of  a  boiler.  Many  people  do  not  realize  that  a  boiler 
forced  beyond  its  capacity  will  not  last  as  long  as  it  would  if  run 
at  normal  ratinsr.     These  stokers  are  good  smoke-consumerx 


120 


STEAM-BOILERS. 


The  ashes  and  clinkers  have  to  be  removed  through  the  fire- 
doors. 


Fig.  49 

Any  stokers  to  which  air  is  admitted  in  this  way,  if  improperly 
handled,  may  give  a  blowpipe  effect.  This  is  due  to  the  air 
escaping  through  the  coal  in  one  spot  instead  of  being  distributed 
through  the  entire  mass  of  coal. 


SETTINGS,  FURNACES,  AND   CHIMNEYS.  121 


122  STEAM-BOILERS. 

The  heat  generated  by  this  action  is  localized  and  very  in- 
tense. 

The  Jones  Under-fed  Stoker. — This  stoker,  shown  by 
Fig.  49,  is  similar  in  its  action  to  the  American.  Air  is  forced 
into  the  ash-pit  in  this  case.  Coal  is  forced  in  intermittently  by 
a  steam  piston.  This  piston  may  be  operated  by  a  hand-lever, 
or  it  may  be  timed  to  operate  as  many  times  an  hour  as  the 
timing  device  is  set  for. 

The  Green  Traveling  Link-grate. — Chain  grates  have 
been  used  to  a  considerable  extent  with  the  poorer  grades  of 
soft  coal.  Fig.  50  illustrates  the  Green  traveling  grate  applied 
to  a  Heine  boiler. 

Power  from  a  shaft  overhead  oscillates  the  vertical  rod  at  the 
left  of  the  cut.  A  ratchet  carried  by  the  arm  moved  by  this  rod 
gives  motion  to  a  train  of  gears.  The  link-grate  is  moved  by 
sprocket-wheels  keyed  to  the  shaft  at  the  extreme  left  of  the 
figure.  The  entire  grate  and  frame  may  be  withdrawn  from  the 
furnace. 

Smoke  Prevention  has  become  a  matter  of  great  social 
importance  in  cities  where  much  smoky  coal  is  used.  Though 
the  loss  through  imperfect  combustion  of  carbon  to  the  form 
of  carbon  monoxide  may  be  great,  and  though  there  may  be 
an  appreciable  loss  if  the  volatile  parts  of  coal  are  driven  off 
unconsumed,  it  is  a  fact  that  the  loss  in  smoke,  even  when  it 
is  dense  and  black,  is  not  enough  to  induce  coal  users  to  take 
the  trouble  to  prevent  the  formation  of  smoke.  Not  infre- 
quently it  has  been  found  that  the  methods  used  to  prevent 
smoke  are  accompanied  by  a  loss  instead  of  a  gain.  For  ex- 
ample, smoke  burning  by  the  alternate  firing  of  two  furnaces, 
leading  to  a  common  combustion-chamber,  may  give  a  slightly 
greater  efficiency  if  just  enough  hot  air  in  excess  is  admitted 
through  the  clear  fire,  to  burn  the  gases  distilled  from  the  fresh 
charge.  If  the  clear  fire  must  be  kept  too  thin,  and  thus 
admit  a  large  amount  of  air,  in  order  that  the  smoke  may  be 
burned,  there  will   be  a  loss  of  efficiency.      Though  it   is  not 


SETTINGS,  FURNACES,  AND   CHIMNEYS.  123 

well  proved,  it  is  asserted  that  the  mixture  of  finely  divided 
carbon,  in  the  form  of  smoke,  with  carbon  dioxide  may  give  a 
clear  gas  with  the  formation  of  carbon  monoxide,  and  thus  with 
a  notable  loss.  The  same  difficulties  arise  when  side  firmer 
and  coking  are  resorted  to  with  smoky  fuels. 

One  of  the  most  perfect  arrangements  for  smoke  prevention 
which  has  yet  been  tried,  consisted  of  a  detached  furnace  with 
small  grate-area  and  a  deficient  air-supply,  so  that  the  coal  was 
distilled  and  burned  to  carbon  monoxide ;  the  resulting  hot 
gases  were  then  burned  under  a  steam-boiler.  The  method 
was  suggested  by  the  producer-furnaces  used  for  making  gas  for 
the  open-hearth  process  of  steel-making.  The  objections  are 
the  loss  of  heat  by  radiation  from  the  detached  furnace  and  the 
space  occupied  by  that  furnace.  Though  reported  to  be  a 
success  so  far  as  the  prevention  of  smoke  was  concerned,  it 
does  not  meet  with  approval. 

It  is  a  common  experience,  that  when  laws  against  making 
smoke  are  enforced,  users  of  fuel  have  chosen  to  buy  anthra- 
cite coal  or  coke,  or  in  some  cases  have  used  crude  petroleum 
oil. 

Down-draught  Furnaces. — In  connection  with  the  sub- 
ject of  smoke  prevention,  attention  should  be  called  to  down- 
draught  furnaces,  which  have  the  connection  with  the  chimnev 
below  the  grate.  The  supply  of  air  is  through  the  fire-door 
to  the  top  of  the  fire,  which  has  a  very  attractive  appearance, 
as  it  burns  brightly  at  the  upper  surface  unless  obscured  by 
fresh  fuel.  A  natural  inference  is,  that  the  combustion  is  per- 
fect in  a  down-draught  furnace,  and  that  it  should  give  a  not- 
able gain  in  economy  of  fuel,  but  a  little  consideration  shows 
that  such  a  furnace  is  subject  to  the  same  conditions  as  an  ordi- 
nary furnace.  If  there  is  either  an  excess  or  a  deficiencv  of  air, 
the  combustion  will  be  imperfect;  in  the  latter  case,  as  with  an 
ordinary  furnace,  smoke  may  appear  at  the  top  of  the  chimnev. 
Tests  made  on  a  boiler  using  first  an  ordinarv  and  then  a  down- 


124 


STEAM-BOILERS. 


draught  grate  have  commonly  shown  little  if  any  advantage  in 
favor  of  the  latter. 

Down  draught  furnaces,  if  properly  arranged  and  fired,  can 
be  made  to  burn  inferior  fuels  which  have  a  large  amount  of 
volatile  matter  without  making  much  smoke;  this  may  be  a 
matter  of  great  importance  in  cities  where  laws  against  smoke  are 
enforced. 

Hawley  Down-draught  Furnace. — This  furnace  consists 
of  a  water-grate,  an  ordinary  grate  beneath  the  water-grate,  and 
an  ash-pit  beneath  this.     There  are  three  sets  of  doors. 

The  upper  doors  are  kept  open  nearly  all  of  the  time.  Coal 
is  fired  through  the  upper  doors.  The  coal  next  to  and  in  con- 
tact with  the  water-grate  is  the  hottest,,  and  any  volatile  products 
driven  off  from  the  green  coal  have  to  pass  downward  through 
the  water-grate  and  over  the  tire  on  the  lower  grate  before  escap- 
ing into  the  space  beyond  the  bridge-wall. 

The  lower  grate  is  supplied  with  coal  which  drops  through 
the  water-grate  when  the  slice-bar  is  used.  This  tire  is  what 
would  be  called  a  dirty  fire  and  shows  clinkers  and  ash. 

As  a  general  rule  firemen  are  not  apt  to  keep  a  sufficient 
depth  of  tire  on  this  lower  grate.  A  fire  about  0  inches  thick 
seems  to  give  best  results. 

The  water-grate  adds  a  large  amount  of  very  efficient  heating- 
surface  to  a  boiler,  and  in  consequence  increases  the  capacity  of 
the  boiler  without  reducing  the  economy. 

Oil-burning  Furnaces  have  the  oil  thrown  in  by  sprayers 
or  atomizers,  and  the  oil  burns  in  a  flame  that  is  about  four 
inches  in  diameter  and  two  to  four  feet  long.  The  sprayer 
has  two  conical  converging  tubes,  one  inside  the  other,  some- 
thing like  the  steam  and  water  nozzles  of  a  steam-injector. 
Compressed  air  or  superheated  steam  is  supplied  to  the  inner 
tube,  and  the  oil  is  drawn  through  the  outer  tube  and  thrown 
into  fine  spray  mingled  with  air.  Compressed  air  is  the 
better,  considering  proper  combustion  only,  but  the  great 
convenience  of  usine  steam  near  a  steam-boiler  has  led  to  its 


SETTIXGS,  FURNACES,  AND   CHIMNEYS.  125 

common  use.  The  proportions  of  air  and  oil  may  be  nicely 
regulated,  so  that  perfect  combustion  may  be  secured  without 
smoke. 

In  the  United  States  oil  has  been  used  for  fuel  at  or  near  oil- 
fields, or  in  cities  where  laws  against  smoke  are  enforced. 

The  use  of  oil  for  fuel  on  war-ships  has  received  favorable 
consideration  from  some  authorities,  the  evident  advantages 
being  the  great  calorific  power  of  oil  and  the  case  with  which 
the  fires  may  be  maintained  and  regulated.  The  fact  that  oil 
in  tanks  may  be  set  on  fire  by  explosive  shells  has  prevented 
any  extensive  adoption  of  oil  for  fuel  on  war-ships. 

Oil  for  fuel  should  be  stored  in  tanks  outside  the  fire-room, 
and  if  possible  the  tanks  should  be  lower  than  the  burners. 
The  oil  is  pumped  from  the  tank  to  the  burners  as  required. 
This  is  to  avoid  accidental  flooding  of  the  furnace  and  the  fire- 
room  with  oil,  and  the  attendant  danger  of  conflagration. 
Crude  oil  is  more  dangerous  than  refuse  oil,  since  the  former 
contains  all  the  volatile  components  that  vaporize  at  ordinary 
temperatures  and  form  explosive  mixtures  with  air. 

Induced  Draught  and  Forced  Draught. — When  a  higher 
rate  of  combustion  is  required  than  can  be  had  with  natural 
draught,  resort  is  had  to  forced  draught,  by  aid  of  which  150 
pounds  of  coal  can  be  burned  per  square  foot  of  grate-surface 
per  hour. 

Three  systems  of  forced  draught  are  in  common  use, 
namely,  with  a  closed  stoke-hole,  with  closed  ash-pits,  and  in- 
duced draught. 

Induced  draught  has  long  been  used  on  locomotives,  by 
the  action  of  the  exhaust-steam  thrown  through  the  smoke- 
stack. The  same  method  is  used  to  some  extent  on  tug- 
boats. This  method  is  simple  and  effective,  but  can  be  used 
only  with  non-condensing  engines.  Induced  draught  may  be 
obtained  by  a  centrifugal,  or  other  form  of  blower,  in  the 
chimney.  It  is  essential  that  an  economizer  should  be  used 
to  cool  the  gases  before  they  come  to  the  blower. 


1 2  6  STEA  M -BOILERS. 

On  steamships  forced  draught  has  been  obtained  by  the 
aid  of  centrifugal  fan-blowers.  The  method  with  closed  ash- 
pit has  been  used  with  success  on  merchant  steamers  and 
some  war-ships.  With  this  method  air  drawn  from  the  fire- 
room  passes  through  a  blower  and  is  delivered  to  the  ash- 
pit, which  has  an  air-tight  door.  If  the  pressure  in  the  ash- 
pit exceeds  the  resistance  to  the  passage  of  air  through  the 
fuel,  flame  comes  out  around  the  fire-door  unless  it  is  also 
made  air-tight.  When  the  fire-door  is  opened  to  throw  on  coal 
the  blast  must  be  shut  off  from  that  furnace  and  all  others 
having  a  common  combustion-chamber,  or  flame  will  shoot 
out  into  the  fire-room  in  a  dangerous  manner.  One  reason 
why  it  has  not  been  used  on  war-ships  is  the  difficulty  of 
properly  ventilating  the  many  small  fire-rooms  in  which  boil- 
ers are  placed. 

The  closed  stoke-hole  has  been  the  customary  way  of  get- 
ting a  forced  draught  on  torpedo-boats  and  on  other  naval 
vessels.  The  stoke-hole  is  closed  air-tight,  admission  and 
egress  being  through  air-locks,  and  air  from  without  is  forced 
in  through  a  centrifugal  blower  till  the  pressure  exceeds  that 
of  the  atmosphere.  When  a  fire-door  is  opened  to  attend  to 
the  fire,  there  is  a  strong  inrush  of  air  that  is  liable  to  make 
the  tube-plates  leak.  So  great  difficulty  has  been  experienced- 
from  this  cause,  when  forced  draught  has  been  used  with  the 
Scotch  boiler,  that  many  naval  officers  doubt  its  advisability 
for  large  ships.  The  success  of  forced  draught  on  the  loco- 
motive and  on  torpedo-boats  with  modified  locomotive-boilers 
may  be  attributed  partly  to  the  type  of  the  boiler  and  partly 
to  the  fact  that  there  is  only  one  boiler  and  one  furnace. 
When  two  boilers  are  used  on  a  torpedo-boat,  each  has  its 
own   chimney. 

On  locomotives  the  induced  draught  is  frequently  equiva- 
lent to  a  column  of  water  five  or  seven  inches  high.  Forced 
draught  on  torpedo-boats  has  approached  those  figures,  but  is 
usually  less.      Large  ships  usually  have  the  forced  draught  re- 


SETTINGS,  FURNACES,  AND   CHIMNEYS.  127 

stricted  to  two  inches  of  water.  On  account  of  the  resistance 
to  the  entrance  of  air  to  the  fire-rooms  of  war-ships,  through 
ventilating  shafts,  gratings,  etc.,  it  has  been  common  to  assist 
the  draught  by  running  the  blowers  without  closing  the  air- 
locks. 

The  increased  cost  of  coal  has  led  many  to  burn  screenings  or 
buckwheat  coal  by  means  of  a  forced  draught. 

A  blower  driven  by  a  steam-engine  supplies  air  to  the  ash-pit 
at  from  12  to  4  inches  water  pressure.  A  rapid  rate  of  com- 
bustion is  maintained,  and  even  though  the  -cheap  coal  is  not 
burned  as  economically  as  it  might  be,  still  the  poorer  coal  at 
the  present  prices  shows  a  saving  in  the  cost  of  making  steam. 

The  speed  of  the  engine  driving  the  blower  is  controlled  by 
the  pressure  in  the  boiler,  a  damper  regulator  operating  the 
throttle  of  the  engine.  When  the  damper  regulator  has  closed 
the  throttle,  the  engine  is  kept  turning  fast  enough  to  pass  the 
dead-centers  by  stean\  admitted  through  a  small  pipe  with  valve, 
which  by-passes  the  throttle  controlled  bv  steam  pressure. 

In  the  induced  draught  system,  as  arranged  in  large  plants, 
the  gases  are  drawn  from  the  grate  through  an  economizer  into 
the  exhaust-fan,  which  then  discharges  the  gases  at  about  3000  F. 
into  the  stack.     The  stack  serves  simply  to  carry  the  gases  away. 

Howden's  System. — The  temperature  of  gases  in  the  up- 
takes of  marine  boilers  is  frequently  high,  especially  when  forced 
draught  is  used.  In  Howden's  system  the  products  of  com- 
bustion pass  through  vertical  transverse  tubes  placed  in  an  en- 
largement of  the  uptake.  Air  to  supply  the  tire  is  forced  over 
these  tubes  by  a  fan-blower  and  is  thereby  warmed,  thus  saving 
heat  and  giving  quicker  combustion.  Care  must  be  taken  in 
using  this  system  not  to  go  too  far,  or  the  fire  may  become  too  hot 
and  rapidly  burn  out  the  fire-grates  and  do  other  injurv. 

Fire  Cracks. — Fire  cracks  are  often  found  on  old  boilers 
at  the  joints  exposed  to  the  fire.  The  two  rivets  at  the  left  in 
Fig.  51  show  such  cracks. 

These  cracks  are  caused  by  the  repeated  buckling,  between 


I2< 


STE.lM-Bi'ILERS. 


the  rivets,  of  the  plate  exposed  to  the  fire.  This  plate  becomes 
much  hotter  than  the  plate  back  of  it  which  is  in  contact  with 
the  water  in  the  boiler,  and  any  change  in  the  temperature  of  the 
fire  is  felt  by  the  plate. 

Innumerable  repetitions  of  this  action  ultimately  starts  a 
crack  which  extends  as  shown.  If  a  crack  extends  beyond  a 
rivet  it  should  be  plugged  to  prevent  the  crack  from  extending 
to  the  edge  of  the  lap  of  the  other  plate.  This  plug  is  a  piece  of 
soft  copper  driven  into  a  hole  drilled  about  3/8  inch  diameter. 

The  cracks  are  most  always  at  the  rivets,  but  sometimes  a 
crack  will  be  found  between  two  rivets. 


Fig.  51. 

In  case  a  fire  crack  should  leak  much  the  leak  may  be  stopped 
for  a  time  by  countersinking  the  plate,  as  shown  by  the  right- 
hand  rivet  and  driving  in  a  very  soft  rivet.  The  metal  of  the 
rivet  will  flow  out  into  the  crack. 

Cleaning  Fires. — Three  tools  are  used  in  clearing  the 
grate:  they  are  a  long  straight  bar  known  as  the  slice-bar,  a 
similar  bar  with  the  point  bent  at  right  angles  to  make  a  hook, 
and  a  long-handled  rake  with  three  or  four  prongs.  The  hook 
may  be  run  along  between  the  grate-bars  from  below,  to  clear 
the  spaces  from  ashes  and  clinker.  The  slice-bar  is  thrust  under 
the  fire  on  top  of  the  grate  to  break  up  the  cinder;  it  is  used  also 
to  stir  and  break  up  caking  coals.  The  rake  is  used  to  haul 
the  fire  forward  or  to  draw  out  cinder. 


SETTINGS,  FURNACES,  AND    CHI  MX  FA'S.  129 

To  clean  a  fire  the  fireman  breaks  up  the  cinder  with  the 
slice-bar  and  rattles  down  the  ashes;  if  necessary,  he  works  the 
fire  back  toward  the  bridge  and  exposes  the  grate  in  front,  which 
may  then  be  thoroughly  cleaned.  Then  he  hauls  the  fire  forward 
and  cleans  the  back  end  of  the  furnace.  Cinder  which  will  not 
break  up  and  pass  through  the  grate  is  pulled  out  through  the 
fire-door.  Some  firemen  prefer  to  clean  the  grate  one  side  at  a 
time.  After  the  grate  is  cleaned  the  fuel  left  is  spread  evenly  over 
the  grate  and  fresh  fuel  is  thrown  on.  The  tire  should  be  allowed 
to  burn  down  before  cleaning,  but  a  fair  amount  of  glowing 
coal  should  be  left  to  start  a  new  fire  briskly.  Before  beginning 
to  clean  the  fire  the  draught  should  be  checked  by  closing  dampers 
or  otherwise. 

Economizers. — An  economizer  consists  of  a  series  of  ver- 
tical cast-iron  tubes  placed  in  the  flue  of  a  boiler  between  the 
boiler  and  the  stack  and  used  to  heat  the  feed-water  with  heat 
recovered  from  the  flue-gases. 

Any  heat  taken  up  in  this  way  is  just  so  much  heat  gained, 
provided  the  draught  is  not  so  reduced  by  the  extra  resistance 
offered  to  the  passage  of  the  flue-gas  as  to  lessen  the  capacity  of 
the  boiler. 

An  economizer  will  show  a  greater  saving  on  a  plant  which  is 
forced  than  on  a  plant  which  is  running  at  a  moderate  rate. 
Ordinarily  a  saving  of  from  8  to  10  per  cent  will  be  made.  It  is 
not  advisable,  however,  to  install  economizers  on  small  plants. 

Soot  is  removed  from  the  outside  of  the  tubes  by  scrapers  in 
the  shape  of  rings  which  are  drawn  over  the  tubes  by  power. 

There  must  be  two  flues:  one  through  the  economizer  con- 
necting with  the  chimney  and  one  leading  directly  from  the  boiler 
to  the  chimney. 

Suitable  dampers  are  located  so  as  to  send  the  gases  through 
either  flue.  This  makes  it  possible  to  repair  the  economizer 
while  the  boilers  are  running. 

The  heat  taken  up  by  the  economizers  of  large  boiler-planis 
.may  be  the  equivalent  of  four  or  five  hundred  horse-power. 


^ — -  ^ 


SETTINGS,   FURNACES,  AND    CHIMNEYS. 


13l 


CROSS  SECTION 


Fig.  53. 


13 : 


STEAM-BOILERS. 


Should  the  economizer  be  disabled  the  power  of  the  boilers 
would  be  reduced  by  this  amount.  This  has  led  to  the  use  of 
what  are  known  as  unit  economizers,  small  economizers,  one  for 
each  boiler  or  for  each  battery  of  two  boilers. 

Feed-water  enters  the  economizer  at  the  end  nearest  the 
chimney  and  leaves  at  the  end  nearest  the  boiler  where  the  gases 
are  hottest.  The  feed-water  is  generally  pumped  through  the 
economizer  directly  to  the  boiler,  thus  putting  the  economizer 
under  boiler  pressure.  In  some  instances,  city  water  under  40 
pounds  pressure  is  taken  through  the  economizer  into  the  pump. 
The  tubes  are  generally  4  inches  inside  diameter  and  about 
9  feet  long.     They  are  arranged  in  groups. 

It  is  customary  to  leave  a  space  9  inches  wide  on  each  side 
between  the  tubes  and  the  brickwork  on  large  economizers  and 
on  one  side  on  small  economizers  to  enable  a  man  to  inspect  the 
tubes.     These  passages  are  closed  by  dampers. 

From  4  to  5  square  feet  of  heating-surface  are  allowed  per 
boiler  horse-power  in  most  cases.  Economizers  are  made  by  the 
Green  Fuel  Economizer  Co.,  and  by  the  B.  F.  Sturtevant  Co. 
Figs.  52  and  53  show  two  different  arrangements  of  the  Green 
economizer. 

Chimneys. — There  are  a  number  of  different  kinds  of  chim- 
neys in  use  to-day,  the  red-brick  stack,  the  radial  brick  stack, 
the  self-supporting  steel  stack,  the  guyed  steel  stack,  and  concrete 
chimneys. 

The  steel  chimneys  are  sometimes  lined  with  fire-brick  and 
sometimes  unlined. 

The  life  of  a  steel  chimney  depends  upon  the  care  taken  of 
it;  probably  ten  to  twelve  years  is  a  fair  estimate  of  the  life  of 
such  a  chimney.  A  steel  chimney  deteriorates  much  more  rapidly 
when  idle  than  when  in  use.  A  brick  stack  lasts  a  great  many 
years. 

Radial  brick  chimneys  are  made  of  a  special  brick,  much 
larger  and  thicker  than  the  ordinary  red  brick,  shaped  to  the 
curve  of  the  chimnev  on  two  faces  and  radial  on  two  faces. 


SETTINGS,  FURNACES,  AND    CHIMNEYS. 


*33 


There  are  five  or  six  holes  about  1  inch  square  running  ver- 
tically through  these  bricks. 

Radial  brick  chimneys  are  very  numerous  in  Germany. 
Many  are  being  built  now  in  this  country.  They  are  known 
here  as  the  Custodis,  the  Heinicke,  and  the  Kellogg  chimneys. 

Concrete  reinforced  by  iron  bars  has  been  used  for  chimneys 
during  the  last  few  years.  It  has  not  always  proved  to  be  a 
success,  in  some  cases,  because  of  faulty  design,  in  others,  because 
of  poor  material  and  poor  construction. 

Various  formulas  have  been  proposed  for  use  in  finding  the 
diameter  and  the  height  of  a  chimney  needed  for  a  given  power, 
those  given  by  Kent,  by  Christie,  and  by  Gale  being  best  known. 

The  following  table,  figured  by  William  Kent  from  his  formula, 
is  borne  out  by  practice.  The  table  is  figured  on  the  assumption 
that  5  pounds  of  coal  are  required  per  boiler  horse-power.  If 
less  coal  is  required  the  capacity  of  the  chimney  is  increased,  and 

SIZES   OF    CHIMNEYS    WITH    APPROPRIATE    HORSE-POWER    OF 

BOILERS. 


Diam- 
eter in 
Inche-. 


24 
27 
3° 
33 
36 
39 
42 
4S 
54 
60 
66 
72 
78 
84 
00 
96 
102 
108 
114 

Z20 
126 
132 
138 
144 


Ft. 


Height  of  Chimneys  and  Commercial  Horse-power. 


60 
Ft. 


38 

5  4 

02 


7° 

Feet. 


80 
Feet. 


27 

41 

5« 

78 

100 

125 

152 

183 

216 


go         1  cc 
Feet.    Feet 


no       125 
Feet.   F>et. 


Feet 


200 
Feet.    Feet. 


Side  of  Actual 

\  ri  1 
Squat 


»q  re. 

Inches 


62 
83 
107 
133 
163 
196 
231 
311 
363 
505 


113 
141 
173 
208 
245 
330 
427 
5  36 
658 
792 


182 

219 

2581 

348 

449 

565 

604 

00  5 

I  163 

1344 
1537 


2-  I 

3°5 

472 
503 

876 

1038 

T  214       1204 


6  ;2 
7i 


r>02 


934     i°32 

lie;      1  2  1  : 


141  ; 
1616 


1496      1639 

ro46     -■  1  -  ■ 
24C2 

5642 

3001 

4  s?7 


2  1  .,  2 
24  50 


748 

01  s 

1 310 

1  5  3  I 
,  _.c 

2027 

2  ;c; 

2594 

:o:  ; 
5230 

! 
3035 

43  T  1 
4-      - 


Il8l 
I4OO 

1^37 
1803 
2167 
2462 
277  j 
3003 
34  5  2 
382b 
420  c 
4605 
5031 


16 

10 

22 
24 
27 
3° 
32 

35 

38 

43 

48 

54 

59 

64 

70 

75 

80 

86 

00 

06 

101 

106 

1 12 

117 

122 

127 


Fee  1 . 


1  ,  77 
2.41 
3    '4 

40i 

504 

7.07 

8.30 

9.  62 

1 2  ■  5  7 

15    go 

19.  04 

23.76 

• 
3  3.l8 

44     18 

50.  2- 

56    75 

-      -- 

86.  ;o 
05.03 

103   S6 
113    10 


134  STEAM-BOILERS. 

its  new  rating  may  be  obtained  by  multiplying  the  figure  given 
in  the  table  by  5  and  dividing  by  the  actual  coal  used  per  boiler 
horse-power. 

Chimney  Draught.— The  draught  produced  by  a  chimney 
is  due  to  the  fact  that  the  gases  inside  the  chimney  are  hotter 
and  consequently  lighter  than  the  outside  air.  Though  these 
gases  at  a  given  temperature  and  pressure  have  a  little  greater 
specific  gravity  than  air  at  the  same  temperature  and  pressure, 
the  difference  is  not  much,  and  may  be  neglected  in  the  dis- 
cussion of  chimney  draught. 

To  get  an  idea  of  the  production  of  draught  by  a  chimney, 
we  may  consider  the  conditions  that  would  exist  if  a  chimney 
were  filled  with  hot  air  and  closed  at  the  bottom  by  a  horizon- 
tal partition  or  diaphragm.  The  pressure  of  the  air  at  the  top 
of  the  chimney,  due  to  the  atmosphere  above  that  level,  is  the 
same  on  the  gases  inside  the  chimney  and  the  air  outside.  The 
pressure  on  the  diaphragm  at  the  bottom  is  the  sum  of  the 
pressure  at  the  top  of  the  chimney  and  of  the  pressure  due  to 
the  column  of  hot  air  in  the  chimney.  At  the  under  side  of 
the  diaphragm  the  pressure  will  be  that  at  the  top  of  the 
chimney  plus  the  pressure  due  to  a  column  of  cold  air  as  high 
as  the  chimney.  This  difference  of  pressure  is  considered  to 
be  the  draught,  in  all  theories  of  the  chimney.  It  may  be 
readily  calculated  for  an  assumed  set  of  conditions.  For  an 
actual  chimney  the  draught  or  difference  of  pressure  inside 
and  outside  the  chimney  may  be  shown  by  a  U  tube  partially 
filled  with  water,  and  having  one  end  connected  to  the  inside 
of  the  chimney  and  the  other  open  to  the  air.  The  water 
rises  in  the  leg  connected  with  the  inside  of  the  chimney ;  the 
difference  of  level  measures  the  draught. 

Suppose  now  that  a  small  hole  is  opened  in  the  dia- 
phragm at  the  bottom  of  the  chimney :  cold  air  from  without, 
under  the  greater  pressure  existing  there,  will  enter  and  will 
force  some  of  the  hot  air  out  at  the  top  of  the  chimney.  If  the 
air  is  heated  as  it  enters,  to  the  temperature  in  the  chimney, 


SETTINGS,  FURNACES,  AND   CHIMNEYS.  135 

we  shall  have  a  continuous  flow  of  cold  air  into  and  of  hot  air 
out  of  the  chimney.  Replacing  the  diaphragm  by  a  grate 
charged  with  burning  fuel,  through  which  cold  air  enters  and 
burns  with  the  fuel,  we  have  the  actual  conditions  of  chimney 
draught. 

For  an  example^  we  will  calculate  the  difference  of  pres- 
sures, or  draught,  if  a  chimney  100  feet  high  is  filled  with  air 
(or  gas)  at  5000  F.,  while  the  temperature  outside  is  6o°  F. 

The  weight  of  a  cubic  foot  of  air  at  320  F.  and  at  the 
average  pressure  of  the  atmosphere  (14.7  pounds)  is  about 
0.0807  °f  a  pound.  Now  the  weight  of  air  at  a  given  pressure 
is  inversely  proportional  to  the  absolute  temperature,  that  is, 
to  a  temperature  obtained  by  adding  459°.5  to  the  temperature 
given  by  a  Fahrenheit  thermometer.  Consequently  we  have 
for  the  weights  of  a  cubic  foot  of  hot  gas  and  of  a  cubic  foot 
of  cold  air : 

Hot  gas,  0.0807  X   459'5+32  =0.041  3; 

Cold  air,  0.0807  X  459'5+j2    =0.0764. 
459.5  +  60 

A  column  of  hot  gas  100  feet  high*  and  1  foot  square  will 
weigh  4.13  pounds,  and  would  give  that  pressure  in  pounds 
per  square  foot  on  a  diaphragm  at  the  bottom  of  the  chimney. 
The  cold  air  outside  will  give  a  pressure  of  7.64  pounds  per 
square  foot.     The  difference  of  pressure  or  draught  will  be 

7.64-4-i3  =  3-5I 
pounds  per  square  foot, 

or  3.51^144  =  0.0242 

of  a  pound  per  square  inch.     In  this  calculation  the  variation 
of  the  pressure  of  the  atmosphere  from  14.7  pounds  per  square 


136  STEAM-BOILERS. 

inch,  and  the  effect  of  the  reduction  of  pressure  in  the  chimney, 
have  been  neglected,  as  they  are  insignificant. 

To  find  the  draught  in  inches  of  water  we  may  consider  that 
one  cubic  foot  of  water  weighs  62.4  pounds.  Consequently  a 
column  of  water  a  foot  square  and  which  produces  a  pressure  of 
3.51  pounds  per  square  foot  will  be 

3.51^62.4  =  0.0562 
of  a  foot  high,  er 

0.0562X12=0.675 

of  an  inch  high.     This  is  the  draught  that  would  be  shown  by 
a  U-tube  if  the  chimney  were  closed  at  the  bottom. 

Areas  of  Chimneys  and  Flues. — In  common  practice  it  is 
found  that  satisfactory  results  are  obtained  if  the  area  of  the 
section  of  a  chimney  is  made  1/10  the  area  of  all  of  the  grates 
connected  to  the  chimney. 

The  area  of  a  chimney  used  for  a  small  plant  where  there  is 
only  one  or  two  boilers  should  be  made  18  the  area  of  the  grate. 

The  flue  and  uptake  of  a  boiler  is  generally  made  1/7  to  1/8 
the  grate  area. 

Forms  of  Chimneys. — Chimneys  are  made  of  brick  or  of 
steel  plates.  Steel  chimneys  are  always  round;  large  brick 
chimneys  are  usually  round;  small  ones  may  be  round  or  square. 
A  round  chimney  gives  a  larger  draught-area  for  the  same  weight 
of  material,  and  it  presents  less  resistance  to  the  wind. 

Plate  V  gives  the  general  arrangement  and  some  detail  of 
two  chimnevs:  one  of  brick,  175  feet  high,  and  the  other  of 
steel,  200  feet  high.  The  brick  chimney  is  built  in  two  parts: 
the  outer  shell,  which  resists  the  pressure  of  the  wind ;  and  the 
lining,  which  forms  the  flue  proper,  and  which  may  expand 
when  the  chimney  is  full  of  hot  gases  without  bringing  any 
stress  on  the  shell.  The  shell  has  a  foundation  of  rough  stone 
and  one  course  of  dressed  stone  at  the  surface  of  the  ground. 
The  brickwork  is  splayed  out  inside  to  cover  the  stone  foun- 


SETTINGS    FURNACES,  AND    CHIMNEYS.  137 

dation,  and  is  drawn  in  at  the  top  to  the  same  diameter  as  the 
inside  of  the  lining.  The  external  form  of  the  top  is  mainly 
a  matter  of  appearance.  The  finish  of  large  tiles  at  the  top 
sheds  rain  and  keeps  water  from  penetrating  the  brickwork. 
The  outside  of  the  shell  has  a  straight  taper  from  the  base 
nearly  up  to  the  head.  A  system  of  internal  buttresses,  as 
shown  in  section  at  Fig.  3  and  Fig.  4,  gives  the  requisite  stiff- 
ness to  the  shell  without  an  excessive  amount  of  materia!. 
The  lining  carries  its  own  weight  only,  being  protected  from 
the  wind  by  the  external  shell;  it  has  a  uniform  diameter  of 
6  feet  inside,  and  varies  in  thickness  from  12  inches  at  the 
bottom  to  4  inches  at  the  top.  A  rectangular  flue  with  an 
arched  top,  leads  into  the  chimney  at  one  side  of  the  founda- 
tion. 

The  shell  of  the  steel  chimney  is  made  of  vertical  half-inch 
plates  at  the  base,  and  is  splayed  out  to  give  additional  bearing 
on  the  foundation.      Above  this  portion  the  shell  has  a  straight 
taper  to  the  top ;  the  plates,  each  4  feet  wide,  vary  in  thick- 
ness from  3/8  of  an  inch  to   1/4  of  an  inch.      At  the  top  an 
external  finish  of  light  plate  is  given  for  the  sake  of  appear- 
ance.     The  foundation  is  of  red  brick,  with  a  course  of  stone 
at  the  surface  of  the  ground,  clamped  by  a  wrought-iron  strap. 
The  shell  is  bolted  through  a  foundation-ring  made  of  cast-iron 
segments  4  inches  thick,  and  a  steel  plate  2\  inches  thick,  by 
long  bolts  which   take    hold   of   anchor-plates  bedded   in   the 
foundation.      The  lining  of   fire-brick  varies  in  thickness  from 
18  inches  at  the  bottom  to  4^  inches  at  the  top.      It  lies  against 
and  is  carried  by  the  steel  shell.      The  internal  diameter  of  the 
chimney  is  intended  to  be  10  feet ;  at  places  the  size  is  a  little 
larger  on  account  of  the  arrangement  of  the  lining.     The  lining 
is  used  to  check  the  escape  of  heat  through  the  steel  shell. 
It  adds  nothing  to  the  strength  of  the  chimnev ;  on  the  con- 
trary, it  must  be  carried  by  the  shell       There  is  a  chance  that 
moisture  may  be  harbored  between   the  lining  ana  the  shell 
and  give  rise  to  corrosion.      Large  steel  chimneys  are  compar- 


T38  STEAM-BOILERS. 

atively  recent,  so  that  experience  does  not  show  whether  lined 
or  unlined  chimneys  are  the  more  durable. 

Stability  of  Chimneys.— On  account  of  the  concentration 
of  weight  on  a  small  area,  and  the  disastrous  results  that  would 
follow  from  defective  work,  the  founaations  of  an  important 
chimney  should  be  carefully  laid  by  an  experienced  engineer. 
A  natural  foundation  is  to  be  preferred,  but  piling  and  other 
artificial  methods  of  preoaring  the  earth  for  the  foundation  can 
be  used  when  necessary.  Good  natural  earth  should  carry 
from  2000  to  4000  pounds  to  the  square  foot.  The  base  of 
the  chimney  should  be  spread  out  so  that  this  pressure,  or 
whatever  the  earth  can  safely  bear,  may  not  be  exceeded. 

In  calculating  the  stability  of  a  chimney  it  is  customary 
to  assume  the  maximum  pressure  01  the  wind  as  55  pounds 
per  square  foot  on  a  flat  surface.  The  pressure  of  the  wind 
on  a  round  chimney  would  theoretically  be  two  thirds  of  that  on 
a  square  chimney.  It  is  commonly  assumed,  however,  that  the 
pressure  on  a  round  chimney  is  0.57  of  that  on  a  square  chimney 
of  the  same  width;  on  a  hexagonal  0.75  and  on  an  octagonal  0.65. 
This  method  has  long  been  in  use,  and  it  has  been  shown  to 
give  abundant  stability.  Experiments  on  wind-pressure  are 
difficult  and  uncertain,  and,  curiously,  the  pressure  determined 
by  small  gauges  is  commonly  in  excess  of  that  shown  by  large 
gauges.  Thus,  certain  experiments  made  during  the  construc- 
tion of  the  Forth  Bridge,  gave  a  maximum  wind-pressure  of 
35  pounds  per  square  foot  on  a  large  gauge  20  feet  long  and 
15  feet  wide,  while  a  small  gauge  showed  a  pressure  of  41  pounds 
at  the  same  time.  The  highest  recorded  pressure  during  violent 
gales,  at  the  Forth  Bridge,  was  that  just  quoted,  namely  35 
pounds  to  the  square  foot.  Small  wind-gauges  have  shown 
a  pressure  of  80  to  100  pounds  to  the  square  foot;  but  such 
results  are  discredited,  both  because  it  is  known  that  small 
gauges  give  too  large  results,  and  because  buildings  were  not 
destroyed  as  they  would  have  been  if  exposed  to  such  wind- 
pressures. 


SETTINGS:  FURNACES,  AXD   CHIMNEYS.  130 

To  determine  whether  a  chimney  is  stable,  treat  it  as  a 
cantilever  uniformly  loaded  with  55  pounds  to  the  square 
foot  and  find  the  bending-moments  and  resultant  stresses. 
The  stress  will  be  a  tension  at  the  windward  side  and  a  com- 
pression at  the  leeward  side.  Calculate  the  direct  stress  due 
to  the  weight  of  the  chimney,  which  will  be  a  compression  at 
either  side  of  the  chimney.  For  a  brick  chimney,  subtract 
the  tension  due  to  wind-pressure  at  the  windward  side  from 
the  compression  due  to  weight :  if  there  is  a  positive  remainder 
showing  a  resultant  compression  the  chimney  will  be  stable ; 
otherwise  not,  because  masonry  cannot  withstand  tension. 
Again,  add  the  compression  due  to  wind-pressure  to  the  com- 
pression due  to  weight,  to  find  the  total  compression  at  the 
leeward  side  :  if  the  result  is  not  greater  than  the  safe  load  on 
masonry,  the  chimney  is  strong  enough.  The  safe  load  may 
be  taken  as  10  tons  per  square  foot. 

Fig.  54  gives  a  graphical  method  of  arriving  at  the  stability 
of  a  chimney.  At  the  point  .4,  the  centre  of  gravity  of  the  trape- 
zoidal area  against  which  the  wind  presses,  a  line  is  drawn  at 
some  convenient  scale  to  represent  the  total  wind-pressure  on  the 
side.  From  B  a  line  BW,  drawn  at  the  same  scale,  represents 
the  total  weight  of  the  chimney. 

Combine  at  point  B  these  two  forces,  and  if  the  resultant  cuts 
the  base  at  a  point  D,  so  that  CD  is  less  than  1/3  EE  for  square 
chimneys  and  less  than  1/4  EE  for  round  chimneys,  there  will  be 
no  tension  on  the  mortar  at  the  windward  side,  and  the  maximum 
intensity  of  compression  will  be  twice  the  mean  intensitv. 

In  the  upper  diagram  at  the  right  of  the  cut  of  the  chimney 
the  line  YY  represents  the  direct  compression  due  to  the  weight 
of  the  chimney;  the  line  XX  the  stresses  due  to  the  action  of 
the  wind.  Combining  these  the  line  ZZ  is  obtained.  This 
shows  at  the  windward  side  a  compression  equal  to  EZ. 

The  second  diagram  illustrates  the  case  where  the  action  of 
the  wind  just  removes  the  compression  at  the  windward  edge, 
making  EZ  at  the  leeward  edge  equal  to  twice  EY. 


140 


STEAM-BOILERS. 


The  third  cut  shows  a  possible  distribution  of  the  stresses  on 
a  section  which  had  cracked  on  the  windward  side. 

The  calculation  for  the  strength  of  a  self-supporting  steel 
chimney  involves  certain  details  of  the  design  of  a  riveted  joint 
and  certain  nice  discriminations  as  to  the  action  of  such  a  joint 


Fig.  54. 


when  affected  by  a  bending  moment,  which  are  out  of  place 
here.  For  example,  it  is  clear  that  on  the  leeward  side  the  com- 
pression on  a  lapped  joint  must  be  borne  by  the  rivets  and  that 
the  plate  between  the  rivets  is  free  from  stress.  A  crude  calcu- 
lation may  be  made  as  for  a  homogeneous  cylinder,  which  is 
subjected  to  compression  and  bending,   using  for  the   apparent 


SETTINGS,  FURNACES,  AND    CHINNEYS. 


141 


working  stress  the  safe  stress  of  the  steel,  multiplied  by  the  effi- 
ciency of  the  riveted  joint,  as  determined  by  methods  given  in 
Chapter  VIII. 

A  calculation  like  that  just  described  must  be  made  for  the 


Fig.  55. 


section  of  the  chimney  at  the  base,  for  each  section  where  there 
is  a  change  of  thickness  or  of  construction,  and  for  any  other 
section  where-  there  is  reason  to  suspect  weakness  or  instab- 
ility. 

A  steel  base  built  up  from  boiler-plate  is  shown  by  Fig.  55. 
This  differs  from  the  one  shown  on  Plate  V. 


142  STEAM  BOILERS. 

The  lining  of  a  brick  chimney  is  to  be  calculated  for  com- 
pression due  to  weight,  at  the  base  and  at  each  section  where 
there  is  a  reduction  of  thickness.  The  lining  of  a  steel  chim- 
ney must  be  counted  in  when  the  stress  due  to  weight  is 
determined. 

A  separate  calculation  must  be  made  for  the  stability  of 
the  foundation  of  a  steel  chimney.  For  this  purpose  find  the 
total  wind-pressure  on  the  chimney  and  its  moment  about  an 
axis  in  the  plane  of  the  base  of  the  foundation.  Find  also 
the  total  weight  of  the  entire  chimney  with  its  lining,  and  of 
the  foundation  :  this  will  be  a  vertical  force  acting  through 
the  middle  of  the  foundation.  Divide  the  moment  of  the 
wind-pressure  by  the  weight  of  the  chimney  and  foundation: 
the  result  will  be  the  distance  from  the  middle  of  the  founda- 
tion to  the  resultant  force  due  to  the  combined  action  of 
wind-pressure  and  weight.  If  this  resultant  force  is  inside 
the  middle  third  of  the  width  of  the  foundation,  the  chimney 
will  be  stable. 

This  brief  statement  is  intended  to  describe  the  method 
of  calculating  the  stability  of  chimneys,  and  not  to  give  full 
instructions.  The  design  and  calculation  for  an  important 
chimney  should  be  intrusted  only  to  a  competent  engineer 
who  has  had  experience  in  such  work. 

The  subject  of  chimneys  is  discussed  quite  fully  and  many 
drawings  given  in  a  work  by  Mr.  W.  W.  Christie  on  "Chimney 
Design." 


CHAPTER   VI. 
POWER   OF    BOILERS. 

The  power  of  a  boiler  to  make  steam  depends  on  the 
amount  of  heat  generated  in  the  furnace,  and  on  the  propor- 
tion of  that  heat  which  is  transferred  to  the  water  in  the 
boiler.  The  amount  of  heat  generated  depends  on  the  size 
of  the  grate,  the  rate  of  combustion,  and  the  quality  of  the 
coal  burned.  The  transfer  of  heat  to  the  water  in  the  boiler 
depends  on  the  amount  and  arrangement  of  the  heating-sur- 
face. In  practice  it  is  found  that  each  type  of  boiler  has 
certain  general  proportions  which  give  good  results ;  any 
marked  variation  from  these  proportions  is  likely  to  give  poor 
economy  in  the  use  of  coal,  or  to  lead  to  excessive  expense  in 
construction. 

The  capacity  of  a  boiler  is  commonly  stated  in  boiler 
horse-power;  the  economy  of  a  boiler  is  given  in  the  pounds 
of  steam  made  per  pound  of  coal.  Neither  method  is  entirely 
satisfactory,  but  definite  meaning  is  attached  to  the  terms 
by  definitions  and  conventions. 

Standard  Fuel. — A  comparison  of  the  composition  and 
of  the  total  heats  of  the  several  kinds  of  coal  given  in  the 
table  on  page  51  shows  a  great  difference  in  the  value  of  a 
pound  of  coal,  depending  on  the  district  and  mine  from  which 
it  comes.  In  order  to  introduce  some  system  into  the  com- 
parison of  the  performance  of  boilers  in  different  localities  it 
has  been  proposed  that  some  coal  or  coals  be  selected  as 
standards,  and  that  all  boiler-tests  intended  for  comparison 
be  made  with  a  standard  coal.      For  this  purpose  it  has  been 

143 


144  STEAM  BOILERS. 

proposed  to  select  Lehigh  Valley  anthracite,  Pocahontas 
semi-bituminous,  and  Pittsburg  bituminous  coal.  More  def- 
inite comparisons  would  result  if  only  one  coal,  such  as  Poca- 
hontas, were  selected.  The  objections  are,  first,  that  some 
trouble  and  expense  might  be  incurred  in  localities  where 
this  coal  is  not  regularly  on  the  market ;  and  second,  that 
a  furnace  designed  for  a  given  coal  may  not  give  its  best 
results  with  a  different  kind  of  coal.  There  is  a  notable  dif- 
ference between  furnaces  designed  for  anthracite  coal  and 
those  designed  for  bituminous  coal ;  for  the  rest  it  appears 
that  the  use  of  a  standard  coal  is  a  question  merely  of  ex- 
pediency. 

In  making  a  boiler-test  it  is  not  difficult  to  make  an  ap- 
proximate determination  of  the  per  cent  of  ash  in  the  coal 
used.  When  that  is  done,  the  economy  is  usually  stated  in 
terms  of  water  evaporated  per  pound  of  combustible,  as  well 
as  per  pound  of  coal.  This  gives  somewhat  more  definite- 
ness  to  the  statement;  but  as  no  account  is  taken  of  the  vola- 
tile matter  in  the  coal,  nor  of  the  oxygen,  this  method  also  is 
indefinite. 

Value  of  Coal. — The  actual  value  of  a  coal  for  making 
steam  can  be  determined  only  by  accurate  tests  with  a  fur- 
nace and  boiler  which  are  adapted  to  develop  and  use  the 
heat  that  the  coal  can  produce.  While  many  boiler-tests 
have  been  made,  and  there  is  a  good  deal  of  material  that 
could  be  used  for  the  purpose,  there  has  not  yet  been  made  a 
satisfactory  statement  of  the  value  of  the  fuel  in  common  use. 

It  appears  probable  that  the  real  value  of  a  coal  for  mak- 
ing steam  is  proportional  to  the  total  heat  of  combustion.  II 
this  can  be  shown  to  be  true,  then  coals  should  be  sold  on  the 
basis  of  heat  of  combustion,  just  as  steel  is  required  to  have 
certain  physical  properties  which  are  determined  by  making 
proper  tests. 

Quality  of  Steam. — When  the  economy  of  a  boiler  is 
stated  in  terms  of  water  evaporated  per  pound  of  coal,  it  is 
*vsumed  that    all  the  water    is    evaporated  into  dry  saturated 


POWER  OF  BOILERS.  145 

steam.      But  the  steam  which  leaves  the  boiler  may  contain 
some  water,  or- it  may  be  superheated. 

The  moisture  carried  along  by  steam  is  called  priming. 
The  steam  from  a  properly  designed  boiler,  working  within  its 
capacity,  seldom  carries  more  than  three  per  cent  of  priming. 
Under  favorable  circumstances  steam  from  a  boiler  will  be 
nearly  dry. 

If  steam,  after  it  passes  away  from  the  water  in  the  boiler, 
passes  over  hot  surfaces  it  will  be  superheated  ;  that  is,  raised 
to  a  temperature  higher  than  that  of  saturated  steam  at  the 
same  pressure.  Vertical  boilers  with  tubes  through  the  steam- 
space  give  superheated  steam.  If  steam  is  to  be  superheated 
to  any  considerable  extent,  it  must  be  passed  through  a 
superheater,  either  attached  or  independently-fired,  as  described 
in  Chapter  II.  Boilers  of  the  Manning  type  and  boilers  equipped 
with  attached  superheaters  generally  give  more  superheat  when 
forced.  This  is  because  of  the  higher  temperature  of  the  escaping 
gases. 

Although  the  consumption  of  an  engine,  figured  on  pounds  of 
steam,  is  less  with  superheated  steam  than  with  saturated  steam, 
it  does  not  necessarily  follow  that  the  coal  per  indicated  horse- 
power per  hour  is  less.  A  number  of  plants  investigated  by  the 
writers  have  shown  an  increased  coal  consumption. 

Certain  types  of  turbine  must  be  supplied  with  superheated 
steam,  if  any  economy  is  to  be  obtained,  on  account  of  the  fact 
that  any  water  in  the  shape  of  priming  in  the  steam  or  any  water 
resulting  from  the  expansion  of  the  steam  acts  like  a  water-brake. 
In  some  turbines  it  is  estimated  that  one  per  cent  priming  causes 
two  per  cent  loss  in  economy. 

Steam-space. — The  steam-space  and  the  free  surface  for 
the  disengagement  of  steam  should  be  sufficient  to  provide  for 
the  efficient  separation  of  the  steam  from  the  water.  Cylin- 
drical tubular  boilers  frequently  have  the  steam-space  equal  to 
one  third  of  the  volume  of  the  boiler-shell.  Marine  return- 
tube  boilers  usually  have  a  smaller  ratio  of  steam-space  to 
water-space. 


1AJ  STEAM  BOILERS. 

The  more  logical  way  appears  to  be  to  proportion  the 
steam-space  to  the  rate  of  steam-consumption  by  the  engine. 
Thus  the  ratio  of  the  volume  of  the  steam-space  of  cylindri- 
cal boilers  to  that  of  the  high-pressure  cylinder  of  multiple- 
expansion  engines  varies  from  50  :  1  to  140  :  1.  The  ratio  of 
the  steam-space  of  a  simple  locomotive-engine  to  the  volume 
of  the  two  cylinders  is  about  6k  :  I. 

The  capacity  of  the  steam-space  is  sometimes  equal  to  the 
volume  of  steam  consumed  by  the  engine  in  20  seconds.  It 
was  found  in  some  experiments  with  marine  boilers  having  a 
working-pressure  less  than  50  pounds  per  square  inch,  that  a 
considerable  quantity  of  water  was  carried  away  by  the  steam 
when  the  steam-space  was  equal  to  the  volume  of  steam  con- 
sumed in  12  seconds,  but  that  no  water  was  carried  into  the 
cylinders  when  the  steam-space  was  equal  to  the  volume  of 
steam  used  in  15  seconds  and  that  no  trouble  from  water  was 
ever  experienced  when  the  steam-space  was  proportioned  for 
20  seconds. 

All  the  preceding  discussion  refers  to  engines  that  run  at  a 
considerable  speed  of  rotation — not  less  than  60  revolutions 
per  minute.  Engines  that  make  but  few  revolutions  per  min- 
ute and  take  steam  for  only  a  portion  of  the  stroke  require  a 
larger  proportion  of  steam-space.  As  an  example  we  may 
cite  the  walking-beam  engines  for  paddle-steamers. 

Equivalent  Evaporation. — The  heat  required  to  evapo- 
rate a  pound  of  water  depends  on  the  temperature  of  the  feed- 
water,  the  pressure  of  the  steam,  and  the  per  cent  of  priming. 

For  example,  if  water  is  supplied  to  a  boiler  at  1400  F., 
and  is  evaporated  under  the  pressure  of  80.3  pounds  by  the 
gauge,  with  2  per  cent  of  priming,  the  heat  required  will  be 
calculated  as  follows: 

The  heat  of  the  liquid  at  1400  F.,  or  the  heat  required  to 
raise  a  pound  of  water  from  320  F.  to  that  temperature,  is 
108.0  B.  T.  U.  The  heat  of  the  liquid  at  95  pounds  abso- 
lute,   corresponding    to    80.3    pounds   by  the    gauge,    is    294.6 


POWER  OF  BOILERS  147 

B.  T.  U.     Consequently  the  heat  required  to  raise  the  feed-water 
up  to  the  temperature  of  the  boiler  is 

294.0-  [08.0=  186.0  B.  T.  U. 

The  heat  of  vaporization,  or  the  heat  required  to  change  a 
pound  of  water  into  steam,  at  95.0  pounds  absolute,  is  890.5 
B.T.  U.  But  2  per  cent  of  water  is  found  in  the  steam  which 
comes  from  the  boiler,  leaving  98  per  cent  of  steam;  consequently 
the  heat  required  is 

0.97  X890.5  =872.7  B.  T.  U. 

The  total  amount  of  heat  is  therefore 

186.6+872.7  =  1059.3  B.T.  U. 

Suppose  that  each  pound  of  coal  evaporates  9  pounds  of  water, 
then  the  heat  per  pound  of  coal  transferred  to  the  boiler  is 

9X1059.3=9534  B.T.  U. 

Now  the  heat  required  to  vaporize  a  pound  of  water  at  2120 
F.,  under  the  pressure  of  the  atmosphere,  is  969.7  B.  T.  U. 
Dividing  the  thermal  units  per  pound  of  coal  by  this  quantity 
gives 

9534^969.7=9.83, 

which  is  called  the  equivalent  evaporation  from  and  at  2120  F. 

This  method  of  stating  the  economy  of  a  boiler  is  equivalent 
to  using  a  special  thermal  unit  969.7  as  large  as  the  thermal  unit 
defined  on  page  54. 

In  making  calculations  involving  quantities  of  wet  steam 
it  is  convenient  to  consider  the  amount  of  steam  present, 
rather  than  the  percent  of  priming.  In  the  example  just  con- 
sidered, there  are  O.02  of  water  or  priming,  and  0.98  of  steam. 
The  part  of  a  pound  which  is  steam  is  represented  by  x. 

If  the  heat  of  vaporization  at  the  pressure  of  the  steam  in 
the  boiler  is  represented  by  r,  the  heat  of  the  liquid  at  that 
pressure  by  q,  and  the  heat  of  the  liquid  at  the  temperature 
of  the  feed-water  by  qa ;    and  if,  further,  there  are  w  pounds  of 


T48  STEAM-BOILERS. 

water    evaporated    per  pound  of  coal, — then    the   equivalent 
evaporation  is 

w{xr  -f  q  —  g„) 
969.7 

The  highest  equivalent  evaporation  per  pound  of  coal  is 
about  12  pounds,  and  to  accomplish  this  result  about  80  per  cent 
of  the  total  heat  of  combustion  must  be  transferred  to  the  water 
in  the  boiler.  The  complete  combustion  of  a  pound  of  carbon 
develops  14,650  B.  T.  U.  ;  if  all  this  heat  could  be  applied  to 
vaporizing  water  at  2120  F.,  then  the  amount  of  water  evap- 
orated would  be 

14,650  -;-  969.7  =  1 5  — ■ —  pounds. 

Few,  if  any,  coals  have  a  greater  heat  of  combustion,  con- 
sequently this  figure  may  be  considered  to  be  the  maximum 
equivalent  evaporative  power  of  coal. 

Should  any  test  appear  to  give  a  larger  evaporative  power, 
or  even  a  power  approaching  this  result,  it  may  be  concluded 
either  that  there  is  an  error  in  the  test,  or  that  there  is  a  large 
amount  of  priming  in  the  steam.  Some  tests  of  early  forms 
of  water-tube  boilers  without  proper  provisions  for  separating 
water  from  the  steam,  appeared  to  give  extraordinary  results; 
which  results  were  due  to  the  presence  of  a  large  amount  of 
priming  in  the  steam.  At  that  time  the  methods  used  for 
determining  the  amount  of  priming  were  difficult  and  uncer- 
tain, and  were  frequently  omitted  in  making  boiler-tests. 

Boiler  Horse-power — It  has  always  been  the  habit  to 
rate  and  sell  boilers  by  the  horse- power.  The  custom  appears 
to  be  due  to  Watt,  and  at  that  time  the  horse-power  of  a 
boiler  agreed  very  well  with  the  power  of  the  engine  with 
which  it  was  associated.  The  traditional  method  of  rating 
boilers,  coming  down  from  that  time,  was  to  consider  a  cubic 
foot,  or  62^  pounds  per  hour,  of  water  evaporated  into  steam, 


POWER  OF  BOILERS. 


140 


as  equivalent  to  one  boiler  horse-power.  This  rating  is  now 
antiquated,  and  is  seldom  or  never  used. 

It  is  now  customary  to  consider  30  pounds  of  water  evap- 
orated per  hour  from  a  temperature  of  ioo°  F.,  under  the 
pressure  of  70  pounds  by  the  gauge,  as  equivalent  to  one 
horse-power.  This  standard  was  recommended  by  a  com- 
mittee of  the  American  Society  of  Mechanical  Engineers.* 

This  standard  is  equivalent  to  the  vaporization  of  34.5 
pounds  of  water  per  hour  from  and  at  2  12°  F.  ;  it  is  frequently 
so  quoted.      It  is  also  equivalent  to  33,470  B.  T.  U.  per  hour. 

Since  the  power  from  steam  is  developed  in  the  engine, 
and  since  the  economy  in  the  use  of  steam  depends  on  the 
engine  only,  and  may  vary  widely  with  the  type  of  engine,  it 
appears  illogical  to  assign  horse-power  to  a  boiler.  The 
method  appears  to  be  justified  by  custom  and  convenience. 

Rate  of  Combustion. — The  rate  of  combustion  is  stated 
in  pounds  of  coal  burned  per  square  foot  of  grate-surface  per 
hour.  It  varies  with  the  draught,  the  kind  of  coal,  and  the 
skill  of  the  fireman. 

In  general  a  slow  or  moderate  rate  of  combustion  gives 
the  best  results,  both  because  the  combustion  is  more  likely 
to  be  complete  and  because  the  heating-surface  of  the  boiler 
can  then  take  up  a  larger  portion  of  the  heat  generated.  A 
very  slow  rate  of  combustion  may  be  uneconomical,  because 
there  is  a  large  excess  of  air  admitted  through  the  grate,  and 
because  there  is  a  larger  proportionate  loss  of  heat  by  radia- 
tion and  conduction.  It  is  claimed  that  forced  draught  may 
be  made  to  give  complete  combustion  with  a  small  amount  of 
air  in  excess,  and  that  it  should  give  better  economy  than 
slower  combustion.  It  will  be  remembered  that  a  small 
amount  of  carbon  monoxide  due  to  incomplete  combustion 
will  cause  more  loss  than  a  large  amount  of  air  in  excess. 

Heating-surface. — All   the    area    of    the    shell,   flues,    or 

"•  Trans.,  voi.  vi,  1&81. 


150  STEM-BOILERS. 

tubes  of  a  boiler  which  is  covered  by  water,  and  exposed 
to  hot  gases,  is  considered  to  be  heating-surface.  Any 
surface  above  the  water-line  and  exposed  to  hot  gases  is 
counted  as  superheating-surface.  The  upper  ends  of  tubes 
of  vertical  boilers  are  in  this  condition. 

For  a  cylindrical  tubular  boiler  the  heating-surface  in- 
cludes all  that  part  of  the  cylindrical  shell  which  is  below  the 
supports  at  the  side  walls,  the  rear  tube-plate  up  to  the  brick- 
arch  which  guides  the  gases  into  the  tubes,  and  all  the  inside 
surface  of  the  tubes.  The  front  tube-plate  is  not  counted  as 
heating-surface. 

For  a  vertical  boiler  like  the  Manning  boiler  (page  11) 
the  heating-surface  includes  the  sides  and  crown  of  the  fire- 
box and  all  the  inside  surface  of  the  tubes  up  to  the  water- 
line.  Surface  in  the  tubes  above  the  water-line  is  superheat- 
ing-surface. A  certain  200-H.P.  boiler  of  this  type  has  1380 
square  feet  of  heating-surface  and  470  square  feet  of  super- 
heating-surface. 

The  heating-surface  of  a  locomotive-boiler  consists  of  the 
sides  and  crown  of  the  fire-box  and  the  inside  surface  of  the 
tubes. 

The  heating-surface  of  a  Scotch  boiler  consists  of  the 
surface  of  the  furnace-flues  above  the  grate  and  beyond  the 
bridge,  the  inside  of  the  combustion-chamber,  and  the  inside 
surface  of  the  tubes. 

The  effective  surface  of  any  tube-plate  is  the  surface  re- 
maining after  the  areas  of  the  openings  through  the  tubes  is 
deducted. 

Relative  Value  of  Heating-surface. — A  review  of  the 
kinds  and  conditions  of  heating-surface  in  various  kinds  of 
boilers,  or  even  in  a  particular  boiler,  shows  that  the  value  of 
heating-surface  varies  widely.  It  does  not  appear  possible  to 
assign  values  to  different  kinds  of  heating-surface.  We  will 
note  only  that  surfaces  like  the  shell  of  a  cylindrical  boiler 
over  the  fire,  like  the  inside  of  a  fire-box,  or  like  the  flues  of 


POWER  OF  BOILERS. 


T5l 


a  marine  boiler,  which  are  exposed  to  direct  radiation  from 
the  fire,  are  the  most  energetic  in  their  action.  Surfaces 
like  combustion-chambers  and  tube-plates,  against  which  the 
flames  play,  are  nearly  if  not  quite  as  good.  The  inside  of 
small  flues  and  tubes  is  less  favorably  situated,  more  especially 
3-3  the  flame  is,  under  ordinary  conditions,  rapidly  extinguished 
after  it  enters  such  a  flue  or  tube.  The  length  of  the  flame 
in  small  tubes  depends  on  the  draught,  and  with  very  strong 
forced  draught  may  extend  completely  through  tubes  of  some 
length. 

The  value  of  heating-surface  in  a  tube  rapidly  decreases 
with  the  length.  It  is  doubtful  if  there  is  any  advantage  in 
making  the  length  of  a  horizontal  tube  more  than  fifty  times 
the  diameter.  Tubes  of  vertical  boilers  should  have  twice 
that  length. 

Ordinary  Proportions. — The  following  table  gives  the 
ordinary  proportions  of  various  types  of  boilers: 


Type  of  Boiler. 


Lancashire    

Cylindrical  multitubular 
Vertical,  Manning 

Locomotive 

Locomotive  type,  sta 
tionary 

Scotch  marine 

Water-tube  with  cylin 
der  or  drum 

Water -tube  with  sepa 
rator 


0 

£ 

n 

3 

- 

il 

\r. 

Ix, 

-.1 

.-.  - 

1) 

u 

■ 

3 

X 

- 

3 

■Jr. 


8  to     12 
S  to     15 

10  to      20 
SO  tO   120 

average  75 


8  to     15 
35  to    45 

9  to     lS 

j    15  to    67 
( average  20 


25  to  30 
35  to  40 
*4S+  16 

60  to  70 


40  to  45 
30 

35  to  45 

30  to  40 


>  6 

>  a  u 

'o~ 

s* 

3.1,  l< 

< 

!/) 

S  to  10 

O.36 

9  to  10.5 

0.30     | 

9  to  10.5 

O.  23 

6.7  to    8.5 

0.07 

9  to  10.5 

0.30 

7  to    9 

O  .  I  I 

9  to  10.5 

0.2S 

7  to    9 

0.22 

t:  o 

3=0 


7.0 

11. 5 
11 .1 


12.6 

3-3 


11. o 

7-3 


*  48  heating-surface,  16  superheating-surface. 

The  higher  rates  of  evaporative  economy  are  associated 
with  slower  rates  of  combustion  and  with  larger  ratios  of 
heating-surface  to  grate- surface. 


152  STEAM-BOILERS. 

No  attempt  is  made  to  distinguish  the  kind  or  location  of 
heating-surface ;  it  must  be  understood  that  the  ordinary  ar- 
rangements and  proportions  for  the  several  types  are  followed 
if  this  table  is  to  be  used  in  designing  boilers.  For  example, 
it  cannot  be  expected  that  heating-surface  gained  by  length- 
ening the  tubes  of  a  locomotive-boiler  will  add  materially  to 
the  efficiency  of  the  boiler. 

This  table  has  been  compiled  from  a  large  number  of  ex- 
amples, and  may  be  taken  to  represent  current  good  practice. 
The  last  two  columns  giving  the  grate-surface  and  heating- 
surface  have  been  computed  on  the  basis  of  one  horsepower 
for  34.5  pounds  of  water  evaporated  per  hour  from  and  at 
212°  F. 


CHAPTER  VII. 
STAYING  AND  OTHER  DETAILS. 

ALL  plates  of  a  boiler  that  are  not  cylindrical  or  hemispher 
ical  require  staying  to  keep  them  in  shape.  For  example, 
the  cylindrical  shell  of  a  cylindrical  tubular  boiler  does  not 
require  staying,  because  the  internal  pressure  tends  to  keep  it 
cylindrical.  On  the  other  hand,  the  pressure  tends  to  bulge 
out  the  flat  ends,  and  they  must  be  held  in  place  against  that 
pressure. 

Many  different  methods  of  staying  will  be  found  in  the 
different  types  of  boilers  seen  in  practice,  and  there  are  fre- 
quently several  ways  of  staying  the  same  kind  of  a  surface. 
A  few  methods  will  be  described  in  a  general  way.  The 
placing  of  stays  and  arrangement  of  details  is  an  important 
part  of  the  design  of  a  boiler,  and  must  be  worked  out  for  each 
special  design. 

Cylindrical  Tubular  Boiler. — The  parts  of  the  tube-sheets 
at  the  ends  of  a  cylindrical  tubular  boiler,  through  which  the 
tubes  pass,  are  sufficiently  stayed  by  the  tubes  themselves. 
The  flat  ends  above  the  tubes  require  staying.  Also,  if  there 
is  a  manhole  at  the  bottom  of  the  front  end,  the  space  thus 
left  unsupported  requires  staying,  and  there  is  a  corresponding 
space  at  the  back  end. 

An  elaborate  set  of  tests  was  made  by  Messrs.  Yarrow*  and 
Co.,  to  determine  the  holding-power  of  tubes  expanded  into 
a  tube-sheet.     It  was  found  that  from  15,000  to  22,000  pounds 


*  London  Engineering,  Jan.  6,  1893. 

153 


154  STEAM-BOILERS. 

were  required  to  pull  out  a  two-inch  steel  tube ;  in  some  cases 
the  tube  gave  way  by  tension  inside  the  head  into  which  it 
was  expanded. 

The  staying  of  a  flat  surface  consists  essentially  in  hold- 
ing it  against  pressure  at  a  series  of  isolated  points,  which  are 
arranged  in  a  regular  or  symmetrical  pattern.  A  simple  case 
of  staying  is  found  in  the  side  sheets  of  a  locomotive  fire-box. 
Here  the  stays,  which  are  arranged  in  horizontal  and  vertical 
rows,  are  screwed  and  riveted.  If  possible,  the  pitch  or  dis- 
tance between  the  supported  points  should  be  the  same,  but 
this  is  possible  only  when  arranged  in  rows  as  just  men- 
tioned. The  allowable  pitch  depends  on  the  thickness  of 
the  plate.  For  cylindrical  tubular  boilers  the  pitch  of  the 
supported  points  of  the  flat  ends  above  the  tubes  is  3.5  to  5 
inches.  The  outside  fibre-stress  in  the  plate  stayed  may  be 
from  6000  to  9000  pounds  per  square  inch ;  the  calculation  of 
this  stress  involves  a  knowledge  of  the  theory  of  elasticity,  and 
will  be  referred  to  later. 

It  is  not  advisable,  for  this  type  of  boiler,  to  assign  a  sepa- 
rate stay  to  each  supported  point  of  the  flat  surface  under 
discussion,  consequently  the  points  are  grouped,  each  point  of 
the  group  being  riveted  to  some  support  inside  the  boiler, 
and  then  the  supports  are  held  by  proper  stays. 

A  good  method  of  staying  the  flat  end  of  a  cylindrical 
boiler  is  shown  by  Plate  I,  and  also,  with  some  further  details, 
by  Fig.  56.  There  are  two  6-inch  channel-bars  of  proper 
length,  that  are  riveted  to  the  flat  head.  The  rivets  tie  the 
plate  to  the  channel-bars  and  thus  support  the  plate  at  iso- 
lated points.  The  channel-bars  in  their  turn  are  supported  by 
stays  that  run  directly  through  the  boiler  and  have  nuts  and 
washers  at  each  end.  The  channel-bars  act  as  beams,  and  must 
be  capable  of  carrying  the  load  due  to  the  pull  on  the  rivets, 
and  the  through-stays  must  carry  the  loads  on  the  beams. 
A  short  piece  of  angle-iron  is  riveted  to  the  upper  side  of  the 
upper  channel-bar;  it  carries  five  additional  rivets  in  the  flat 


STAYING  AND  OTHER  DETAILS. 


l^D 


head,  and  adds  an  additional  load  to  the  upper  channel-bar. 
The  points  where  the  through-stays  pass  through  the  head 
are  supported  directly  by  the  stays  through  the  washers  and 
nuts. 

The  lower  channel-bar  >s  a  continuous  girder  with  four  spans 
and  five  supports.  The  stays  form  three  supports  and  the 
other  two  are  at  the  inner  edge  of  the  flange  of  the  head. 
The  upper  channel-bar  is  a  girder  with  three  spans  and  four 


FRONT  HEAD  FOF 

84-3"  TUBES 

Fig.  56. 


supports.  The  calculation  of  the  stresses  in  the  channel- 
bars  is  somewhat  unsatisfactory,  largely  because  the  support 
at  the  flange  of  the  head  is  uncertain;  and  this  support  must 
be  left  with  some  flexibility,  and  consequently  with  soem 
uncertainty,  as  too  great  rigidity  leads  to  grooving. 

In  arranging  .such  a  staying,  we  begin  by  determining  the 
allowable  pitch  of  the  points  supported  by  the  rivets,  assuming 
them  to  be  in  equidistant  horizontal  and  vertical  rows.  This 
allowable  pitch  must  not  be  exceeded,  but  the  pitch  may  be 
made  less  either  horizontally  or  vertically,  or  in  both  ways. 

A  space  of  at  least  three  inches  is  left  between  the  top 


1 56  STEAM-BOILERS. 

row  of  tubes  and  the  lowest  row  of  xivets,  and  a  similar  space 
is  left  at  the  sides.      This  is  to  avoid  grooving. 

The  two  upper  through-stays  are  fifteen  and  a  half  inches 
apart  on  centres.  They  must  be  wide  enough  apart  to  allow 
a  man  to  pass  through. 

The  stay-rods  are  upset  at  the  ends  so  that  the  diameter 
at  the  bottom  of  the  threads  is  greater  than  the  diameter  of 
the  body  of  rod.  The  washer  outside  the  plate  may  be 
made  of  copper,  in  which  case  it  is  made  cup-shaped  so  as  to 
bear  on  a  narrow  ring,  and  is  made  tight  by  calking;  or  the 
washer  is  made  of  iron,  and  is  bedded  in  red  lead  to  make 
a  joint.  Sometimes  cap-nuts  are  used  outside  the  head  to 
prevent  the  escape  of  steam  that  may  leak  around  the  screw- 
threads.  Long  stay-rods  are  sometimes  supported  at  the 
middle. 

A  method  of  staying  otherwise  similar  to  that  just  de- 
scribed, uses  two  angle-irons  in  place  of  a  channel-bar.  A 
washer  of  special  form  is  used  to  give  a  proper  bearing,  for 
the  inner  nut  on  the  through-stay,  against  the  angle-irons. 

Fig.  57  shows  a  different  method  of  staying  for  cylin- 
drical boilers.  The  left  half  of  the  figure  represents  the  end 
elevation,  and  the  right  half  represents  a  section  through  the 
manhole;  this  is  a  common  method  for  boiler  drawings. 
The  supported  points  are  arranged  in  sets  of  four,  and  are 
tied  to  forgings  known  as  crowfeet.  Fig.  58  represents  such 
a  crowfoot  with  four  rivets,  known  as  a  double  crowfoot; 
a  single  crowfoot  with  only  two  rivets  is  shown  by  Fig.  59. 
When  crowfeet  are  used  they  may  be  arranged  in  various 
patterns,  in  the  example  given  there  is  a  horizontal  row  of 
five  double  crowfeet  just  above  the  tubes,  and  three  other 
double  crowfeet  are  arranged  in  a  circular  arc.  At  the  ends 
of  the  arc  there  are  two  braces  like  Fig.  60,  which  are  used 
instead  of  single  crowfeet.  From  each  crowfoot  a  diagonal 
stay  is  carried  to  the  boiler-shell.  These  stays  are  flattened  at 
the  farther  end  and  bent  to  lie  against  the  side  of  the  shell,  to 


STAYING  AXD  OTHER  DETAILS. 


157 


which  they  are  riveted  with  two  or  three  rivets ;    the  arrange- 
ment is  similar  to  that  of  the  right-hand  end    of  the    brace 


c  ) 

O 

.... 

J 

f 

°J 

V   ° 

.... 

Fig.  5S.  Fig.  59. 

shown  by  Fig.  60.      At  the   crowfoot  the  stay  has  a  forked 
head    through   which    a    bolt   passes    under  the    arch    of    the 


158 


STEAM-BOILERS. 


double   crowfoot.     A  nut  holds  the  bolt  in   place  and  pre 
vents  the  head  of  the  stay  from  spreading. 


Fig.  62 
A  combination  of  channel-bar  and  crowfeet  is  shown  by 
Fig.  61.      The  double  crowfeet  are  represented  as  made  of 
boiler-plate,  bent  up  as  shown  by  Fig.  62. 


STAY  IXC  AND  OTIII-.R  DETAILS. 


J59 


A  method  of  staying,  suitable  only  for  boilers  which 
work  under  low  steam-pressure,  is  shown  by  Fig.  63.  Short 
pieces  of  T  iron,  arranged  radially,  are  riveted  to  the  head. 
Each  T  iron  is  supported  from  the  cylindrical  shell  by  two 


OOOOOO  OOOOOO 
OOOOOO  OOOOOO 


Fig.  63. 

diagonal  stays ;  one  of  the  stays  \s  represented  by  Fig.  64. 
One  end  of  the  stay  is  split,  and  is  pinned  to  the  T  iron; 
the  other  end  is  flattened,  and  riveted  to  the  shell. 

The  shell  of  a  cylindrical  boiler,  whether  it  is  a  tubular  or 
a  flue  boiler,  is  made  of  a  series  of  sections  or  rings.      Each 


Fig.  64. 

ring  is  made  of  one  or  two  plates  riveted  along  the  edge,  or 
longitudinal  seam.  This  seam  has  at  least  two  rows  of  rivets; 
more  complicated  joints  are  commonly  used  to  give  more 
strength  to  the  seam.  Alternate  rings  of  the  shell  are  made 
smaller  so  that  they  may  be  slipped  inside  the  rings  at  each 
of  their  ends.  The  seams  joining  adjacent  rings  are  com- 
monly single-riveted.      The  longitudinal  seams  are  kept  above 


t6o  steam-boilers. 

the  middle  of  the  boiler,  so  that  they  are  not  exposed  to  the  fire. 
The  first  ring  at  the  front  end  is  always  an  outside  ring,  so  that 
the  first  ring-seam  has  the  outside  edge  pointing  away  from  the 
fire;  there  is  consequently  less  liability  of  injury  to  the  seam 
from  the  flames  that  pass  under  the  boiler  toward  the  back  end. 

Fig.  65  shows  what  is  known  as  the  Huston  brace.  It  takes 
the  place  of  the  braces  shown  by  Figs.  60,  62,  and  64.  It  is  made 
without  welds. 

All  horizontal  multitubular  boilers,  60  inches  or  over  in  diam- 
eter, should  have  a  manhole  in  the  front  head,  as  shown  by  Fig.  174 
in  Chapter  XII.  The  manhole  frame  is  itself  sufficiently  stiff  to 
reinforce  the  bottom  of  the  front  head,  but  the  back  head  must 


3^ 


Fig.  65. 

be  stayed.  Ten  or  twelve  tubes  must  be  omitted  in  order  to 
make  room  for  the  manhole.  Fig.  66  shows  a  good  method  of 
staying  the  back  head  between  the  tubes  and  the  shell. 

Two  pieces  of  angle  iron  are  riveted  to  the  plate  with  a  dis- 
tance piece  or  ferrule  made  of  a  piece  of  pipe  or  tube  between  the 
plate  and  the  bottom  of  the  angle  irons.  These  ferrules  hold  the 
angle  iron  off  from  the  plate  2  to  3  inches. 

This  distance  allows  of  a  free  circulation  of  water  and  pre- 
vents an  overheating  of  the  plate.  A  space  2  inches  deep  will 
be  sufficiently  great  to  prevent  scale  from  bridging  over  the  space 
between  the  angle  iron  and  the  plate.  Rivets  are  pitched  from 
5  to  8  inches  along  the  angle  irons. 

Bolts  commonly  made  with  tapering  heads  fitting  conical 
holes  in  the  plate  pass  between  the  angle  irons  and  are  drawn 
tight  by  nuts. 

Two  stay-rods  flattened  at  one  end  are  fastened  to  the  angle 
irons,  as  shown.     These  rods  lead  at  a  slight  angle  through  the 


STAYIXG  AXD    OTHER     DETAILS. 


161 


162  .STEAM-BOILERS. 

front  head,  one  at  cither  side  of  the  manhole  frame,  and  are 
fastened  by  nuts.  The  threaded  ends  are  upset  to  a  diameter 
greater  than  the  centre  of  the  rod.  The  angle  at  which  the  rods 
run  across  the  boiler  is  so  slight  that  there  is  no  trouble  with  the 
nuts  at  the  front  head.  These  rods  should  never  be  tied  to  the 
bottom  shell.  Huston  braces  should  not  be  used  or  any  system 
which  ties  to  the  shell. 

Vertical  Boilers. — The  tube-sheets  of  a  vertical  boiler, 
as  is  evident  from  inspection  of  Figs.  6  and  7,  are  usually  stayed 
sufficiently  by  the  tubes.  Should  the  upper  tube-sheet  be  much 
larger  than  the  crown  of  the  fire-box,  it  may  need  staying  be- 
tween the  tubes  and  the  shell.  Stays  like  Fig.  60  may  be  used 
for  this  purpose. 

The  circular  fire-box  of  a  vertical  boiler  is  subjected  to 
external  pressure,  and  rs  prevented  from  collapsing  under  that 
pressure  by  tying  it  to  the  outer  shell  by  screwed  stay-bolts, 
which  are  put  in  and  set  like  the  stay-bolts  for  a  locomotive- 
boiler. 

Locomotive-boiler. — The  parts  of  a  locomotive-boiler 
that  require  staying  are  the  fire-box  and  the  flat  ends.  The 
tube-sheets  are  sufficiently  stayed  by  the  tubes,  but  there  is  a 
part  of  the  tube-sheet  at  the  smoke-box  end  and  a  part  of  the 
flat  end  above  the  fire-box  which  requires  support.  The  prob- 
lems here  resemble  those  met  in  staying  the  tube-sheets  of  a 
horizontal  cylindrical  boiler,  and  similar  methods  are  used. 
Thus  in  Plate  II  there  are  shown  eight  through-stays,  each  l£ 
of  an  inch  in  diameter.  These  stays  pass  through  the  girder 
staying  of  the  crown-sheet,  and  have  a  simple  nut  and  washer 
outside  the  end-plates  of  the  boiler.  At  the  smoke-box  end, 
as  shown  by  Figs.  1  and  3,  Plate  II,  there  are  two  diagonal 
stays  taking  hold  of  single  crowfeet  and  running  to  the  middle 
of  the  barrel.  At  the  fire-box  end  there  are  four  crowfeet  or 
short  angle-irons,  made  by  bending  up  boilerplate;  two  are 
shown  by  the  right-hand  elevation  of  Fig.  2  on  Plate  II.  The 
outer  crowfeet  have  five  rivets,  and  the  others  six.  From  the 
outer  crowfeet  diagonal  stays  run  to  the  shell  at  the  ring  just 


STAYING  AXD  OTHER  DETAILS.  163 

in  front  of  the  fire-box.  From  the  inner  crowfeet  stays  run  to 
the  middle  ring  of  the  boiler.  There  are  also  two  stays  like 
Fig.  60,  which  run  to  the  shell  above  the  fire-box.  Finally, 
there  is  a  crowfoot  and  stay  at  the  middle  of  the  row  of  eight 
through-stays,  this  stay  fastening  to  the  two  end  crown-bars. 

Below  the  tubes  there  is  a  place  in  the  fire-box  tube-sheet 
which  requires  support.  This  is  given  by  three  braces  like 
Fig.  60,  as  shown  by  Figs.  1  and  2,  Plate  II.  The  shell  of 
the  boiler,  shown  by  this  plate,  is  higher  over  the  fire-box  than 
it  is  at  the  barrel,  and  a  ring  of  peculiar  shape  is  required  to 
join  the  two  parts  together.  This  ring  is  cylindrical  below  and 
conical  on  top ;  at  the  sides  there  are  flattened  spaces  which 
require  stiffening  to  prevent  them  from  springing,  and  thus 
start  grooving  of  the  plates.  For  this  purpose  there  are  three 
T  irons  riveted  to  the  shell  at  the  flattened  place  mentioned, 
as  shown  by  Fig.  1,  Plate  II.  The  upper  ends  of  the  T  irons 
on  opposite  sides  of  the  boiler  are  tied  together  by  transverse 
stays  above  the  tubes. 

Coming  now  to  the  fire-DOx  of  the  boiler  represented  by 
Plate  II,  we  find  that  at  the  front,  rear,  and  sides  it  is  tied  to 
the  external  shell  by  screwed  stay-bolts  set  in  equidistant  hor- 
izontal and  vertical  rows.  The  holes  for  these  stay-bolts  are 
punched  or,  better,  drilled  before  the  fire-box  is  in  place.  After 
it  is  in  place  and  riveted  to  the  foundation-ring  a  long  tap  is 
run  through  both  plates,  the  fire-box  plate  and  the  shell,  and 
thus  a  continuous  thread  is  cut  in  the  plates.  A  steel  bolt  is 
now  screwed  through  the  plates,  cut  to  the  proper  length,  and 
riveted  cold  at  each  end.  Owing  to  the  screw-thread  on  the 
bolts,  this  riveting  is  imperfect,  and  likely  to  develop  cracks  at 
the  edge.  The  thread  should  be  removed  from  the  middle 
of  the  bolts,  as  they  are  then  less  liable  to  crack  under  the 
peculiar  strains  set  up  by  the  unequal  expansion  of  the  fire- 
box and  outside  shell. 

The  stay-bolts  are  very  likely  to  be  cracked  or  broken  on 
account  of  the  expansion  of  the  fire-box;   to  detect  such  a 


1 64  steam-boilers. 

failure  of  a  bolt,  or  to  show  when  excessive  corrosion  has  taken 
place,  the  stay-bolts  are  often  drilled  from  the  outer  end  nearly 
through  to  the  inner  end.  In  case  of  failure  steam  will  blow 
out  of  the  defective  stay ;  serious  injury  has  often  been  avoided 
by  this  method. 

The  crown-sheet  of  the  fire-box  is  exposed  to  intense  heat., 
and  is  covered  with  only  a  few  inches  of  water.  The  problem 
of  properly  staying  this  flat  crown-sheet  without  interfering 
with  the  supply  of  water  to  it  is  one  of  the  most  difficult 
problems  in  locomotive-boiler  construction.  Figs.  I  and  2, 
Plate  II,  show  the  method  of  staying  a  crown-sheet  with  a  sys- 
tem of  girder-stays.  Above  the  crown-sheet  there  are  fourteen 
double  girders,  which  are  supported  at  the  ends  by  castings  of 
special  form,  shown  by  Figs.  2  and  6;  the  castings  rest  on  the 
edges  of  the  side  sheets  and  on  the  flange  of  the  crown-sheet* 
In  addition  the  girder-stays  are  slung  to  the  shell  by  sling- 
stays.  At  intervals  of  four  and  a  half  inches  the  crown-sheet 
is  supported  from  the  girders  by  bolts,  having  each  a  head  in- 
side the  fire-box,  as  shown  by  Fig.  5,  and  a  nut  at  the  top 
bearing  on  a  plate  above  the  girder.  These  plates  are  turned 
down  at  the  ends  to  keep  the  two  halves  of  the  girder  from 
spreading.  There  is  a  copper  washer  under  the  head  of  each 
bolt,  inside  the  fire-box,  to  make  a  joint.  Between  the  girder 
and  the  crown-sheet  each  bolt  has  a  conical  washer  or  thimble 
to  maintain  the  proper  distance  between  the  girder  and  crown- 
sheet.  This  thimble  is  wide  above  to  bear  on  the  girder,  and 
small  below  to  avoid  interfering  with  the  flow  of  water  to  the 
crown-sheet,  and  also  so  as  to  cover  as  little  surface  as  possible 
on  account  of  the  danger  of  burning  the  crown-sheet  wherever 
the  metal  is  thickened.  The  whole  system  of  girders  is  tied 
together,  and  the  girder  nearest  the  fire-door  is  tied  to  the 
outside  shell,  thereby  serving  as  stage  for  the  head.  It  is  evi- 
dent that  such  a  system  of  staying  is  heavy,  cumbersome,  and 
complicated.  It  is  also  uncertain  in  its  action,  since  the  equal- 
ization of  stresses  depends  on  a  nice  adjustment  of  the  mem- 


STAYING  AXD  OTHER  DETAILS. 


l6< 


bers  of  the  system,  which  adjustment  is  liable  to  derangement 
from  expansion  of  the  fire-box.  The  girders  or  crown-bars  are 
sometimes  run  lengthwise  instead  of  transversely,  but  as  the 
fire-box  is  longer  than  wide  such  an  arrangement  is  inferior. 

To  avoid  the  cumbersome  method  of  staying  the  crown- 
sheet,  which  has  just  been  described,  the  fire-box  end  of  the 
boiler  has  been  made  flat  on  top,  as  shown  by  Fig.  67.      The 


Fig.  67. 

crown-sheet  can  now  be  stayed  to  the  outside  shell  by  through- 
stays  having  nuts  and  copper  washers  at  each  end.  The  flat 
side  sheets  of  the  shell  above  the  fire-box  are  also  stayed  by 
through-stays,  and  there  are  also  three  longitudinal  through- 
stays  in  the  corners  of  the  shell  over  the  fire-box  where  it 
protrudes  beyond  the  barrel.  This  forms  what  is  known  as 
the  Belpaire  fire-box,  from  the  inventor. 

Fig.  68  shows  an  attempt  to  combine  the  use  of  through- 
stays,  like  those  of  the  Belpair  fire-box.  with  a  cylindrical  top 
above  the  crown-sheet.  It  will  be  noted  that  the  stays  are 
neither  perpendicular  to  the  crown-sheet  nor  radial  when  they 
pierce  the  shell,  and  they  must  be  subjected  to  an  awkward 
side  pull  at  both  places. 

The  locomotive-boiler  represented  by  Plate  III  has  a 
Belpair  fire-box,  and   shows  in  addition   some  peculiarities  of 


1 66 


STEAM-BOILERS. 


staying.  Thus  the  flat  end-plate  above  the  fire-box  has 
four  T  irons  riveted  to  it.  Each  T  iron  is  tied  to  the  shell 
by  two  diagonal  stays.  Each  stay  has  the  usual  double 
head  at  the  T  iron;  the  other  end  lies  between,  and  is  pinned 
to  the  flanges  of  pieces  of  plate  that  are  riveted  to  the  shell 
of  the  boiler.     This  arrangement  is  shown  by  the  transverse 


and  longitudinal  sections  through  the  fire-box.  It  will  be 
noticed  that  the  lower  diagonal  stays  from  the  end-plate 
interfere  with  four  transverse  through-stays.      These  stays  are 


STAYING  AND  OTHER  DETAILS. 


I67 


cut  off  and  carry  short  vertical  yokes,  which  are  connected 
by  two  smaller  rods,  one  above  and  one  below  the  diagonal 
stays. 

The  rings  forming  the  barrel  of  the  locomotive  are  made 
progressively  smaller  from  the  fire-box  to  the  smoke-box;  the 
slight  taper  toward  the  front  end  of  the  locomotive  is  found 
convenient  in  the  design  of  the  machine. 

Fig.  69  shows  two  ways  of  making  the  furnace-mouth  of 
a  locomotive-boiler.  In  one  way  the  end- 
plate  of  the  boiler-shell  and  the  corre- 
sponding plate  of  the  fire-box  are  flanged 
in  the  same  direction,  and  are  riveted  out- 
side of  the  boiler.  In  the  other  case  the 
two  plates  are  flanged  into  the  water-space 
and  the  overlapping  edges*  are  riveted. 

Marine    Boiler. — The    parts    requiring 
staying  in    the    Scotch    boiler  are  the  flat 
ends,    the  furnaces,   and    the    combustion- 
chambers.      The  flat   ends  above  the   tubes 
Fig.  69.  are  stayed  by  through-stays  with  nuts  inside 

and  with  washers  and  nuts  outside  the  plate.  The  boiler 
shown  by  Fig.  n,  page  17,  has  two  rows  of  through-stays 
— four  in  the  upper  and  six  in  the  lower  row;  two  of  the 
upper  row  pass  through  the  fitting  which  carries  the  steam- 
nozzle. 

It  is  found  in  practice  that  the  tube-sheets  of  a  marine 
boiler  are  not  sufficiently  stayed  by  plain  tubes  expanded 
into  the  sheets.  It  is  customary  to  make  a  portion  of  the 
tubes  thicker  than  the  others,  and  to  provide  these  thick 
tubes  with  thin  nuts  outside  the  tube-plates,  so  that  they  may 
act  more  effectively  as  stays.  The  thick  tubes  in  Fig.  11  are 
indicated  by  heavy  circles.  Sometimes  every  other  tube  of 
each  second  row  is  made  a  thick  tube;  that  is,  something 
more  than  one  fourth  of  the  tubes  are  stay-tubes.  Usually 
the  number  is  fewer  than  this. 


m 

& 


1 68  STEAM-BOILERS. 

Below  the  tubes  the  front  plate  is  supported  in  part  by  the 
furnace-flues,  and  in  part  by  through-stays  running  to  the 
combustion-chamber.  There  are  two  such  stays  above  the 
furnaces  and  three  below  the  furnaces  in  the  middle  of  Fig. 
II,  each  if  of  an  inch  in  diameter.  There  are  also  two  stays 
2\  inches  in  diameter,  one  at  each  side  and  above  the  fur- 
naces. These  last  stays  have  one  point  of  attachment  to  the 
front  end-plate,  but  each  has  two  points  of  attachment  to  the 
combustion-chamber.  For  this  purpose  the  rear  ends  of  the 
stays  are  bolted  to  V-shaped  forgings,  similar  to  that  shown 
by  Fig.  70,  page  169. 

The  furnace-flues  are  corrugated  to  stiffen  them,  and  thus 
maintain  their  form  under  the  external  pressure  to  which  they 
are  subjected.  The  corrugations  in  Fig.  11  are  made  up  of 
alternate  convex  and  concave  semicircles;  other  forms  of 
corrugations  and  other  methods  of  stiffening  flues,  together 
with  a  discussion  of  the  strength  of  flues,  will  be  given  in  the 
next  chapter.  The  front  ends  of  the  furnace-flues  in  Fig.  11 
are  made  as  large  as  the  outside  of  the  corrugations;  the  rear 
ends  are  as  small  as  the  inside  of  the  corrugations.  Such  an 
arrangement  makes  it  easv  to  remove  the  furnaces  without 
disturbing  the  other  parts  of  the  boiler  and  without  destroy- 
ing the  flues. 

The  combustion-chambers  of  a  Scotch  boiler  are  made  up 
of  flat  or  curved  plates  subjected  to  external  pressure,  and 
must  be  stayed  at  frequent  intervals  to  prevent  collapsing. 
The  sides  and  bottom  of  the  combustion-chamber  in  Fig.  11 
are  stayed  to  the  cylindrical  shell  of  the  boiler  by  screwed 
stay-bolts,  spaced  seven  inches  on  centres.  The  back  of  the 
combustion-chamber  is  stayed  in  like  manner  to  the  back  end 
of  the  boiler,  and  thus  both  of  these  flat  surfaces  are  secured. 
The  plates  used  for  making  the  combustion-chamber  are 
thicker  than  those  used  for  a  locomotive  fire-box,  and  conse- 
quently the  stays  are  spaced  wider  and  are  larger  in  diameter. 

The   top  of   the  combustion-chamber  is  stayed   by  stay- 


STAYING  AND  OTHER  DETAILS. 


169 


bolts  and  bridges  in  a  manner  that  suggests  the  crown-bar 
staying  of  a  locomotive  fire-box.  The  space  is,  however, 
narrower  and  the  staying  is  less  complicated. 

Complex  Stays. — Sometimes  the  points  to  be  connected 
by  stays  are  so  numerous  that  too  many  through-stays  will  be 


Fk;.  70. 

required  if  all  points  are  stayed  separately.  Thus  in  Fig.  70 
there  is  a  tee-iron  riveted  to  a  flat  plate,  and  supported 
at  intervals,  as  indicated  by  the  two  bolts  passing  through 
it.  Instead  of  using  a  through-stay  for  each  bolt,  the  bolts 
are  coupled  by  two  V-shaped  forgings,  which  forgings  are 
bolted  to  a  through-stay  at  the  angle  of  the  V.  There 
is  enough  freedom  of  the  bolts  in  their  holes  to  give  equal 
distribution  of  the  pull  on  the  through-stay.  By  an  exten- 
sion of  this  method  several  points  may  be  supported  by  one 
stay-rod. 

Gusset-stays. — The  flat  ends  of  the  Lancashire  boiler, 
shown  by  Fig.  4,  page  7,  are  secured  to  the  cylindrical  shell 
by  gusset-stays;  such  a  stay  is  shown  more  in  detail  by  Fig. 
71.      A   plate  is  sheared'  to  the  proper  form,  and   is   riveted 


170 


STEAM-BOILERS. 


between  two  angle-irons  along  the  edges  that  come  against 
the  shell  and  the  flat  end.  The  angle-irons  in  turn  are  riveted 
to  the  shell  or  to  the  flat  plate.  Gusset-stays  have  the 
advantages  of  simplicity  and  solidity.  They  interfere  less 
with  the  accessibility  of  the  boiler  than  through-stays  or 
diagonal  stays.  Their  chief  defect  is  that  they  are  very  rigid 
and  are  apt  to  localize  the  springing  of  the  flat  plates,  which 


Fig.    71, 


is  caused  by  unequal  expansion  of  the  furnace-flues  and  shell. 
Consequently,  grooving  near  gusset-stays  is  very  likely  to  be 
found  in  Lancashire  and  Cornish  boilers.  Gusset-stays  are 
also  used  to  some  extent  in  marine  boilers,  and  in  locomo- 
tive-boilers. 

Spherical  Ends. — The  ends  of  cylindrical  boilers,  or  of 
steam-drums,  are  commonly  curved  to  form  a  spherical  sur- 
face, in  which  case  they  retain  their  form  under  internal 
pressure  and  do  not  need  staying.  If  the  radius  of  the 
spherical  surface  is  equal  to  the  diameter  of  the  cylindrical 
surface,  the  same  thickness  of  plates  may  be  used  for  both. 
If  the  spherical  surface  has  a  longer  radius,  the  thickness  may 
be  increased.  Such  dished  heads  of  boilers  and  steam-drums 
are  struck  up  between  dies  while  at  a  flanging  heat,  and  are 
then  flanged  to  give  a  convenient  riveting  edge. 

Steam-domes  are  short,  vertical  cylinders  of  boiler-plate 
fastened  on  top  of  the  shell  of  horizontal  boilers.  Plates  II 
and  III  show  steam-drums  on  locomotive-boilers.  A  steam- 
drum  may  be  used  to  advantage  when  the  steam-space  is  so 
shallow  that  there  is  danger  that  the  ebullition  may  throw 


STAYING  AND  OTHER  DETAILS.  171 

water  into  the  pipe  leading  steam  from  the  boiler.      Locomo 
tivcs  usually  have  steam-domes,    for  not  only  is  the  steam- 
space  shallow,  but  there   is  danger  of  splashing  of  the  water 
in    the    boiler,    especially    if   the    track    is   rough   or    sharply 
curved. 

Stationary  boilers  ought  to  have  steam-space  enough  with- 
out domes;  marine  boilers  sometimes  have  domes,  but  they 
are  less  common  than  formerly.  The  additional  steam- 
volume  in  a  steam-dome  is  insignificant,  so  that  a  dome  should 
not  be  added  to  increase  steam-space  of  a  boiler. 

The  main  objection  to  a  steam-dome  is  that  it  weakens 
the  boiler-shell,  which  must  be  cut  away  to  form  a  junction 
with  it.  The  shell  may  be  reinforced,  to  make  partial  com- 
pensation, by  a  ring  or  flange  of  boiler-plate.  Such  a  flange 
is  clearly  shown  on  Plate  III,  where  the  longitudinal  seam  of 
the  ring  carrying  the  dome  is  purposely  placed  at  the  top  of 
the  boiler.  A  similar  arrangement  is  made  for  the  dome  on 
Plate  II. 

Dry-pipe. — Any  pipe  inside  of  a  boiler  for  the  purpose  of 
leading  steam  from  the  boiler  is  known  as  a  dry-pipe;  the 
pressure  in  such  a  pipe  is  frequently  less  than  that  of  the 
steam  in  the  boiler,  consequently  there  is  a  tendency  to  dry 
the  steam  in  the  pipe.  Dry-pipes  are  found  in  locomotive 
and  marine  boilers  and  sometimes  in  stationary  boilers. 

The  dry-pipe  of  a  locomotive  opens  near  the  top  of  the 
dome.  It  runs  vertically  down  till  it  is  well  below  the  shell 
of  the  barrel,  then  it  runs  horizontally  through  the  steam- 
space  and  out  through  the  smoke-box  tube-sheet.  The 
throttle-valve  is  at  the  inlet  of  the  dry-pipe.  It  is  controlled 
through  a  bell-crank  lever  by  a  rod  which  enters  the  head  of 
the  boiler  from  the  cab. 

The  marine  boiler  shown  by  Fig.  11  has  a  dry-pipe  which 
is  joined  to  a  steam- nozzle  at  the  front  end  of  the  boiler. 
This  dry-pipe  is  pierced  with  numerous  longitudinal  slits  on 


T72 


STEAM-BOILERS. 


the  upper  side;  the  sum  of  the  area  of  such  slits  is  seven 
eighths  of  the  area  through  the  stop-valve  in  the  steam-pipe. 

Steam-nozzle. — The  stationary  boiler  shown  on  Plate  I 
has  a  cast-iron  steam-nozzle  at  each  end.  The  steam-pipe 
leading  steam  from  the  boiler  is  bolted  to  the  rear  nozzle, 
and  the  safety-valves  are  placed  above  the  front  nozzle. 

Nozzles  are  often  made  of  cast  steel.  The  best  are  forged 
without  welds  from  one  piece  of  steel. 

Manholes. — A  manhole  should  be  large  enough  to  allow 
a  man  to  pass  easily  inside  the  boiler.  That  on  Plate  I  is 
fifteen  inches  long  and  eleven  inches  wide,  and  has  its  greatest 
dimension  across  the  boiler. 

The  manhole  there  shown  is  placed  inside  the  shell  of  the 
boiler.  Both  the  ring  and  the  cover  are  forged  from  steel 
without  a  weld.      Fig.  72    shows  a  form  of  manhole  that  is 


Fig.  72. 

placed  outside  the  shell.  This  form  is  commonly  made  of 
cast  iron,  but  cast  steel  manholes  of  similar  form  are  used  to 
some  extent. 

The  manhole-ring  should  be  strong  enough  to  give  com- 
pensation for  the  plate  cut  away  from  the  ring  on  which  it  is 
placed. 

The  manhole-cover  is  placed  inside  the  ring  so  that  it  is 
held  up  to  its  seat  by  the  steam-pressure.  The  cover  is 
drawn  up  to  its  seat  by  a  bolt  and  removable  yoke.      Some- 


STAYING  AXD  OTHER  DETAILS.  17? 

times  there  are  two  bolts  each  with  its  yoke.  A  cast-ircn 
manhole  naturally  has  a  cast-iron  yoke,  and  a  forged  manhole 
has  a  wrought-iron  or  steel  yoke. 

The  manhole-cover  is  made  steam-tight  by  a  rubber 
gasket;  the  form  of  the  cover  and  its  seat  are  such  that  the 
gasket  cannot  be  blown  out  by  the  pressure  of  the  steam. 

Hand-holes  are  provided  at  various  places  on  boilers  to 
aid  in  washing  out  and  cleaning.  Thus  the  boiler  on  Plate  I 
has  a  hand-hole  near  the  bottom  at  each  end,  and  there  are 
several  hand-holes  near  the  foundation-ring  of  the  vertical 
boiler,  shown  by  Fig.  6.  The  hand-hole  covers  on  Plate  I  are 
placed  directly  against  the  plate  which  is  not  reinforced.  Each 
is  held  up  by  a  bolt  and  a  small  yoke,  which  has  a  bearing  on 
the  plate  completely  round  the  hole.  If  the  yoke  has  insuffi- 
cient bearing  on  the  plate,  the  latter  is  liable  to  be  damaged 
and  leaks  will  occur.  The  hand-holes  on  the  marine  boiler 
shown  by  Fig.  n  are  reinforced  by  small  plates  outside  the 
boiler-heads. 

Washout  Plugs. — Instead  of  hand-holes,  washout  plugs, 
two  inches  or  two  inches  and  a  half  in  diameter,  are  provided 
near  the  corners  of  the  foundation-ring  of  a  locomotive  fire- 
box. Such  plugs  are  simply  screwed  into  the  outside  plate 
of  the  boiler.      Examples  are  shown  by  Plates  II  and  III. 

Methods  of  Supporting  Boilers. — Horizontal  cylindrical 
boilers  are  commonly  supported  on  the  side  walls  of  the  brick 
setting,  by  brackets  which  are  riveted  to  the  shell  of  the 
boiler.  Thus  the  boiler  shown  on  Plate  I  has  two  such 
brackets  on  each  side;  this  boiler  is  about  sixteen  feet  long. 
If  a  boiler  is  as  much  as  eighteen  feet  long,  three  brackets 
are  used.  The  front  brackets  rest  directly  on  the  brickwork, 
but  the  other  brackets  rest  on  iron  rollers,  to  provide  for  the 
expansion  of  the  boiler.  The  brackets  are  set  so  that  the 
plane  of  support  is  a  little  above  the  middle  of  the  boiler. 

Fig.  73  shows  a  common  form  of  bracket,  made  of  cast 
iron,   which  is  riveted  to  the  shell  above  the  flange  of  the 


174 


STEAM-BOILERS. 


bracket.      A  better  form  with  rivets  both  above  and   below 
the  flange  is  shown  by  Fig.  74. 


0  0 

00 

0 

0 

0  0 

00 

0 
0 

0 
0 

' 

k 

000 

Fig. 


Fig. 


74- 


A  detachable   bracket,  like  that  shown   by  Figs.  75   and 
76,  may  be  used  when  the  boiler  must  be  put  into  a  building 


Fig.  75. 

through  a  small  aperture.      Fig.    75  gives  an  end   and  side 
elevation  and  plan  of  the  body  of  the  bracket;  Fig.  76  gives 


Fig.  77.  Fig.   78. 

a  side  elevation  and  plan,  with  section,  of  the  flange.      After 
the  boiler  is  in   place  the  flange  is  thrust  up  into  the  dovetail 


STAYING  AXD  OTHER  DETAILS. 


17" 


groove  in  the  body  of  the  bracket.  The  pressure  of  the  fiance 
against  the  dovetail  groove,  intensified  by  the  wedging  action 
of  the  inclined  sides,  is  liable  to  be  excessive.  To  overcome 
this  difficulty  the  bracket  shown  by  Figs.  77  and  7$  is  often 


Fig.  79. 


0 

0  0 
0  0 

0  0 

Fig.  81.  Fig.  83. 

used.  Fig.  77  shows  the  end  elevation  and  a  view  from 
below,  of  a  casting  which  is  riveted  to  the  shell.  Fig.  78 
shows  the  same  views  of  a  casting  which  catches  into  the 
hollow  under  Fig.  77  and  bears  at  the  top  against  this  same 
casting,  the  rivets  bolting  it  to  the  shell  being  countersunk- 


176 


STEAM-BOILERS. 


Horizontal  boilers,  and  especially  plain  cylindrical  boilers, 
are  sometimes  hung  from  a  support  above  the  boiler,  as  shown 
by  Figs.  79,  80,  and  81. 

Fig.  79  shows  a  lug,  made  of  boiler-plate,  riveted  to  the  shell 
of  the  boiler.  The  lugs  are  placed  in  pairs  and  the  boiler  is 
hung  from  these  lugs  by  bolts  that  are  supported  between  trans- 
verse beams  over  the  boiler.  Fig.  80  differs  in  substituting  a 
loop  for  the  lug. 

Fig.  81  shows  a  method  of  suspension  with  two  short  pieces 


ite 


Fig.  84. 


of  plate  above  the  lug,  to  give  some  flexibility  and  provide  for 
expansion. 

Figs.  82  and  83  show  methods  of  suspending  a  boiler  from 
the  top.  These  methods  are  proper  only  for  boilers  which  have 
a  small  diameter. 

Whenever  possible  it  is  better  to  suspend  a  boiler  rather  than 
to  support  it  by  brackets.  The  top  of  a  bracket  comes  3  or  4 
inches  below  the  longitudinal  joint.  If,  due  to  any  settlement  of 
the  brickwork,  the  bracket  bears  near  its  outer  edge,  there  is  a 
bending  moment  of  considerable  magnitude  transmitted  to  the 
shell. 

This  tendency  to  pull  the  shell  out  just  at  the  bottom  of  the 
bracket  and  to  push  the  shell  in  at  the  top  of  the  bracket  pro- 


STAYING    AND    OTHER    DETAILS. 


•77 


duces  very  severe  strains  in  boilers  of  large  diameter  and  of  great 
weight. 

Boilers  over  20  feet  long  require  three  sets  of  supports. 

If  brackets  are  used  it  is  probable  that  the  middle  set  will 
either  take  more  or  less  than  one  third  the  weight. 

The  proper  way  to  support  such  a  boiler  is  as  shown  in  Fig.  84. 

Three  lugs,  like  Figs.  79  and  80,  or  preferably  like  Fig.  81, 
are  fastened  to  each  side  of  the  boiler.  Rods  from  the  front 
lugs  pass  up  between  two  I-beams,  resting  on  piers  built  up 
above  the  side  walls  of  the  setting,  and  fasten  to  the  beams,  as 
shown. 

Rods  from  the  middle  and  rear  lugs  are  attached  on  each  side 
to  an  equalizer,  which  is  in  turn  hung  from  I-beams  in  the  same 
way  as  at  the  front.  As  these  connections  are  free  to  turn  the 
load  is  always  distributed  in  the  same  proportion  between  the 
lugs. 


CHAPTER   Vm. 
STRENGTH   OF   BOILERS. 

The  determination  of  the  thickness  of  boiler-plates,  the 
size  of  stays,  and  other  elements  affecting  the  strength  of  a 
boiler,  involves  a  knowledge  of  the  properties  of  the  materials 
used  and  a  knowledge  of  the  methods  of  calculating  stresses 
in  the  several  members  of  the  boiler.  A  brief  statement  of 
these  subjects,  as  applied  to  boilers,  will  be  given  here. 

Materials  Used. — The  materials  used  for  making  boilers 
are  mild  steel,  wrought  iron,  cast  iron,  malleable  iron,  copper, 
bronze,  and  brass. 

In  order  to  insure  that  materials  used  for  making  a  boiler 
shall  have  the  proper  qualities,  it  is  customary  to  require  that 
specimens  shall  be  tested  in  a  testing-machine,  and  that  they 
shall  have  certain  definite  properties,  such  as  ultimate  tensile 
strength,  elastic  limit,  and  contraction  of  area  at  fracture. 
In  order  that  these  properties  shall  be  properly  developed,  it 
is  essential  that  specimens  shall  be  of  right  size  and  shape, 
and  that  the  testing  shall  proceed  in  a  correct  method. 

Testing-machines. — The  frame  of  a  testing-machine 
carries  two  heads,  between  which  the  test-piece  is  placed,  and 
to  which  it  is  fastened  by  wedges  or  other  clamping  devices. 
One  head,  called  the  straining-head,  is  drawn  by  screws  or  by 
a  hydraulic  piston,  and  pulls  on  the  test-piece.  The  other 
head,  called  the  weighing-head,  transmits  the  pull  to  some 
weighing  device.  Boiler  materials  are  commonly  tested  in  a 
machine  which  has  the  pull  applied  by  screws,  driven  through 
gearing  by  hand  or  by  power;  the  pull  is  weighed  by  a  system 
of  levers  and  knife-edges,  arranged  like  those  of  a  platform 

178 


STRENGTH   OF  BOILERS.  I  79 

scale.  Such  a  machine  should  be  able  to  exert  a  pull  of  fifty 
or  a  hundred  thousand  pounds. 

Testing-machines  that  give  a  direct  tension  are  commonly 
arranged  to  give  also  a  direct  compression.  There  are  also 
machines  arranged  to  givre  transverse  loads,  like  the  load 
applied  to  a  beam. 

Forms  of  Test-pieces.  ■ —  A  test-piece  of  boiler-plate 
should  be  at  least  one  inch  wide,  planed  on  both  edges,  and 
should  be  about  two  feet  long.  A  piece  which  is  less  than 
eighteen  inches  long  is  not  fit  for  testing. 

Test-pieces  eighteen  inches  to  two  feet  long  may  be  cut 
directly  from  bars  or  rods  for  making  stays  or  bolts.  If  a  rod 
is  so  large  that  the  available  testing-machine  will  not  break 
it,  it  is  of  course  possible  to  turn  it  down  to  a  smaller 
diameter,  but  it  would  be  preferable  to  send  such  a  rod  to  a 
machine  that  is  powerful  enough  to  break  it  at  full  size. 

Test-pieces  of  cast  metal  may  be  cast  in  the  form  of 
rectangular  bars,  which  should  be  at  least  one  inch  wide  and 
an  inch  thick.  If  the  bars  are  rough  or  irregular  it  may  be 
necessary  to  plane  the  edges,  or  perhaps  to  plane  them  all 
over. 

Test-pieces  of  boiler-plate  should  be  cut  from  the  edge 
of  at  least  one  plate  of  each  lot  of  plates.  Sometimes  speci- 
fications require  pieces  from  each  plate  used  for  a  given  boiler. 
Pieces  should  be  cut  from  both  the  side  and  the  end  of  a 
plate,  for  there  is  a  grain  developed  by  rolling  either  iron  or 
steel  boiler-plate,  and  tests  should  be  made  both  with  the 
grain  and  across  the  grain. 

Very  hard  material  may  require  shoulders  on  the  test- 
pieces  to  enable  the  testing-machine  to  get  a  proper  hold. 
But  iron  or  steel  that  is  so  hard  as  to  require  shoulders  is 
much  too  hard  for  boiler-making;  consequently  there  will  be 
no  reason  for  providing  test-pieces  of  boiler  iron  or  steel  with 
shoulders.  If  test-pieces  have  shoulders,  they  should  be  at 
least  ten  inches  apart. 


i8o 


S  TEA  M-B01LERS. 


Methods   of  Testing. — A  test-piece  of  proper  length  is 

first  measured  to  determine  the 
breadth  and  thickness  or  else  the 
diameter,  as  the  case  may  be. 
A  length  of  eight  inches  is  laid 
off  near  the  middle  of  the  test- 
piece,  and  clamps  for  measuring 
the  stretch  of  the  piece  are  ap- 
plied at  the  ends  of  this  eight-inch 
length,  as  shown  by  Fig.  85. 
The  piece  is  then  secured  in  the 
machine  and  a  load  is  applied. 
The  distance  between  the  clamps 
is  now  measured  by  a  micrometer 
caliper  with  an  extension-piece. 
The  method  of  doing  this  is  to 
place  the  head  of  the  micrometer 
against  a  point  on  the  flange  of 
the  clamp  at  one  end,  and  adjust 
the  length  of  the  micrometer  so 
that  it  shall  just  touch  the  cor- 
responding point  on  the  other 
clamp.  A  little  practice  will  en- 
able the  observer  to  measure  to 
one  or  two  ten-thousandths  of  an 
inch.  As  the  load  is  increased 
the  test-piece  stretches,  the  in- 
crease of  length  being  proportion- 
al to  the  increase  of  the  load.  The 
stretch  is  measured  on  both  sides 
of  the  test-piece  for  each  increase 
of  load  applied.  If  the  test-piece 
is  not  straight  or  exactly  aligned 
in  the  machine  there  may  be  some 
irregularity    in    the  stretching  at 


STRENGTH  OF  BOILERS.  l8l 

first,  but  after  a  considerable  load  is  applied  the  piece 
stretches  uniformly  until  about  half  the  maximum  load  that 
the  piece  can  carry  has  been  applied.  During  the  progress 
of  the  test  a  point  is  reached  beyond  which  the  stretch  in 
creases  more  rapidly  than  the  load;  this  is  known  as  the 
elastic  limit. 

After  the  elastic  limit  is  reached  the  clamps  are  removed 
and  the  test  proceeds  without  them,  but  at  about  the  same 
rate  of  loading.  A  load  is  soon  reached  which  the  piece 
cannot  permanently  endure,  shown  by  the  fact  that  the  scale- 
beam  will  fall  though  the  straining-head  remains  at  rest. 
This  is  called  the  yield  point.  The  piece  may,  however, 
carry  a  considerably  higher  load  if  the  straining-head  is  kept 
moving  to  take  up  the  stretch.  Finally,  the  piece  begins  to 
draw  down  rapidly,  somewhere  near  the  middle  of  its  length, 
and  when  the  piece  breaks,  the  fracture  shows  about  half  the 
area  of  the  piece  before  testing.  Hard  materials  may  draw 
down  little,  or  not  at  all;  the  limit  of  elasticity  may  approach 
the  strength  of  the  material. 

The  jaws  or  wedges  of  the  testing-machine  interfere  with 
the  stretching  or  flow  of  the  material  gripped  by  them.  The 
influence  of  the  wedges  may  extend  two  or  three  inches 
beyond  their  edge  in  the  testing  of  boiler-plate.  If  a  piece 
has  shoulders  they  will  have  a  like  effect.  Consequently  the 
points  at  which  a  clamp  is  secured  to  a  test-piece  should  be 
two  or  three  inches  from  a  shoulder  or  from  the  wedges  of  the 
machine.  The  wedges  of  a  machine  of  a  capacity  of  fifty  or 
a  hundred  thousand  pounds  are  four  or  five  inches  long. 
They  will  grip  on  three  inches  at  the  end  of  a  test-piece,  but 
not  on  less.  The  test-piece  must  have  eight  inches  for 
measuring  stretch,  two  or  three  inches  at  each  end  for  flow, 
and  three  to  five  inches  at  each  end  in  the  wedges.  Conse- 
quently the  piece  must  be  eighteen  or  twenty-four  inches 
long. 

The    method   just    described    is   slow   and    laborious,  and 


j  ;_>  STEAM-BOILERS. 

requires  two  observers — one  to  measure  stretch  and  one  to 
weigh.  For  commercial  work  an  automatic  device  is  often 
used  which  registers  loads  and  corresponding  elongations. 
Such  devices  commonly  record  the  yield  point  instead  of  the 
elastic  limit;  these  two  points  should  never  be  confused. 

Stress. — The  number  of  pounds  of  force  per  square  inch 
is  called  the  stress.  The  stress  is  uniform  on  a  piece  under 
direct  tension,  and  is  equal  to  the  load  divided  by  the  area  of 
transverse  section.  Stress  may  be  expressed  in  other  units, 
such  as  tons  per  square  foot  or  kilograms  per  square  milli- 
meter. 

Strain. — The  stretch  of  a  piece,  under  direct  tension,  per 

unit  of  length  is  called  the  strain.      If  the  original  length  is  / 

.     .    a 
and  the  stretch  is  a,  then  the  strain  is  -  =  s. 

The  Limit  of  Elasticity  is  the  limiting  stress  beyond 
which  the  strain  increases  more  rapidly  than  the  stress.  The 
limit  is  not  perfectly  definite,  and  can  be  determined  approxi- 
mately only.  A  load  greater  than  the  elastic  limit  will  pro- 
duce an  appreciable  permanent  elongation  after  the  load  is 
removed.  A  stress  less  than  the  elastic  limit  will  produce 
only  a  slight  permanent  elongation;  such  elongation  may  be 
inappreciable. 

Yield  Point.  —  The  stress  at  which  the  scale-beam  of  a 
testing-machine  will  fall  while  the  straining-head  is  at  rest  is 
called  the  stretch  limit. 

Ultimate  Strength. — The  maximum  stress  that  a  piece 
will  endure  in  a  testing-machine  is  called  the  ultimate  strength 
of  the  material.  The  strength  depends  somewhat  on  the  rate 
of  testing.  The  more  rapidly  the  testing  proceeds  the  higher 
will  be  the  apparent  strength.  It  is  desirable  that  some 
standard  rate  of  testing  may  be  adopted  by  engineers  so  that 
results  may  be  strictly  comparable. 

The  Modulus  of  Elasticity  is  the  result  obtained  by 
dividing  the  stress  by  the  strain.      If  the  stress  is/  pounds 


STRENGTH   OF  BOILERS.  1 83 

per  square  inch  and  the  strain  is  s  per  inch,  then  the  modulus 
of  elasticity  is 

E  =  t 

s 

Reduction  of  Area. — The  area  of  the  test-piece  of  boiler- 
plate at  the  rupture  is  much  less  than  that  of  the  piece  before 
testing.  This  reduction  is  important,  as  it  shows  the  ductility 
of  the  metal,  and  its  ability  to  change  shape  without  too 
much  distress  under  the  influence  of  unequal  expansion  of 
different  members  of  a  boiler. 

Ultimate  Elongation. — After  the  test-piece  is  broken  the 
two  parts  are  laid  down  in  a  straight  line  with  the  broken 
ends  in  contact,  and  the  length  of  the  distance  between  the 
points  of  attachments  of  the  measuring  clamps  is  measured. 
The  ratio  of  the  elongation  to  the  original  length  (eight 
inches)  is  called  the  ultimate  elongation.  The  ultimate  elon- 
gation is  generally  given  in  per  cent.  This  is  important,  for 
the  same  reason  given  for  the  contraction  of  area. 

Compression. — The  preceding  definitions  are  given  for 
tension  only,  for  sake  of  simplicity  and  brevity;  they  may 
be  applied  to  pieces  in  direct  compression  if  the  term  stretch 
or  elongation  is  replaced  by  compression. 

Shearing. — Stresses  have  thus  far  been  considered  to  be 
at  right  angles  to  the  sections  of  the  pieces  to  which  they  are 
applied,  and  produce  either  tension  or  compression  at  that 
section.  A  stress  that  is  not  at  right  angles  to  a  section  will 
tend  to  produce  sliding  at  that  section.  A  stress  that  is 
parallel  to  a  section  will  tend  to  produce  sliding  only,  and  is 
called  a  shearing-stress.  If  a  shearing-stress  is  uniformly  dis- 
tributed, its  intensity  may  be  found  by  dividing  the  total  force 
or  load  by  the  area  of  the  section. 

The  rivets  of  a  riveted  seam  are  subjected  to  a  shearing- 
stress. 


!%4  STEAM-BOILERS. 

Steel  Specifications. — At  the  present  time  all  boiler-plates 
are  made  of  steel. 

The  American  standard  specifications  for  steel  of  the  American 
Society  of  Testing  Materials  are  universally  adopted  in  the  United 
States.  That  part  of  the  specifications  relating  to  boiler  and 
rivet  steel  will  be  quoted  in  full. 

OPEN-HEARTH  BOILER    PLATE  AND   RIVET   STEEL. 
Adopted  1 901. 

Process  of  Manufacture. 

1.  Steel  shall  be  made  by  the  open-hearth  process. 

Chemical  Properties. 

2.  There  shall  be  three  classes  of  open-hearth  boiler-plate 
and  rivet  steel;  namely,  flange  or  boiler  steel,  fire-box  steel,  and 
extra  soft  steel,  which  shall  conform  to  the  following  limits  in 
chemical  composition : 

Flange  or  Fire-box  Extra  Soft 

Boiler  Steel,  Steel,  Steel, 

Per  Cent.  Per  Cent.  Per  Cent. 

_,,.,.,                   ,  f    Acid    0.06       Acid    0.04       Acid    0.04 

Phosphorus  shall  not  exceed |    Bask  QQ4       Basic  Q  ^       BasJc  q  £ 

Sulphur  shall  not  exceed  ...... .'. 0.05  0.04  0.04 

Manganese 0.30  to  0.60     0.30  to  0.50     0.30  to  0.50 

3.  Boiler  Rivet  Steel. — Steel  for  boiler  rivets  shall  be  of  the 
extra  soft  class  as  specified  in  paragraphs  Nos.  2  and  4. 

Physical  Properties. 

4.  Tensile  Tests. — The  three  classes  of  open-hearth  boiler- 
plate and  rivet  steel — namely,  flange  or  boiler  steel,  fire-box 
steel,  and  extra  soft  steel — shall  conform  to  the  following  physical 
qualities: 

Flange  or  Fire-box  Extra  Soft 

Boiler  Steel.  Steel.  Steel. 

Tensile  strength,  lbs.  per  sq.  in.    55,000  to  65,000    52,000  to  62,000    45,000  to  55,000 

Yield-point,  in  lbs.  per  sq.  in., 

shall  not  be  less  than JT.  S.  JT.  S.  JT.  S. 

Elongation,  per  cent  in  8  inches, 

shall  be  net  less  than 25  26  28 


STRENGTH    OF    BOILERS.  185 

5.  Modifications  in  Elongation  for  Thin  and  Thick  Mali  rial. 
— For  material  less  than  five-sixteenths  inch  (5/16")  and  more 
than  three-fourths  inch  (3  '4")  in  thickness  the  following  modi- 
fications shall  be  made  in  the  requirements  for  elongation : 

(a)  For  each  increase  of  one-eighth  inch  (1/8")  in  thickness 
above  three-fourths  inch  (3  4")  a  deduction  of  one  per  cent  1  1%) 
shall  be  made  from  the  specified  elongation. 

(b)  For  each  decrease  of  one-sixteenth  inch  (1/16")  in  thickness 
below  five-sixteenths  inch  (5/16")  a  deduction  of  two  and  one- 
half  per  cent  (2^%)  shall  be  made  from  the  specified  elongation. 

6.  Bending  Tests. — The  three  classes  of  open-hearth  boiler- 
plate and  rivet  steel  shall  conform  to  the  following  bending  tests: 
and  for  this  purpose  the  test  specimen  shall  be  one  and  one-half 
inches  (iV')  wide,  if  possible,  and  for  all  material  three-fourths 
inch  (3/4")  or  less  in  thickness  the  test  specimen  shall  be  of 
the  same  thickness  as  that  of  the  finished  material  from  which 
it  is  cut,  but  for  material  more  than  three-fourths  inch  (34") 
thick  the  bending  test  specimen  may  be  one-half  inch  (1/2")  thick: 

Rivet  rounds  shall  be  tested  of  full  size  as  rolled. 

(c)  Test  specimens  cut  from  the  rolled  material,  as  specified 
above,  shall  be  subjected  to  a  cold  bending  test,  and  also  to  a 
quenched  bending  test.  The  cold  bending  test  shall  be  made 
on  the  material  in  the  condition  in  which  it  is  to  be  used,  and  prior 
to  the  quenched  bending  test  the  specimen  shall  be  heated  to  a 
light  cherry-red,  as  seen  in  the  dark,  and  quenched  in  water  the 
temperature  of  which  is  between  8o°  and  qo°  Fahrenheit. 

(d)  Flange  or  boiler  steel,  fire-box  steel,  and  rivet  steel,  both 
before  and  after  quenching,  shall  bend  cold  one  hundred  and 
eighty  degrees  (i8ocj  flat  on  itself  without  fracture  on  the  outside 
of  the  bent  portion. 

7.  Homogeneity  Tests. — For  fire-box  steel  a  sample  taken  from 
a  broken  tensile  test  specimen  shall  not  show  any  single  seam  or 
cavity  more  than  one-fourth  inch  (1/4")  long  in  either  of  the 
three  fracutres  obtained  on  the  test  for  homogeneity  as  described 
below  in  paragraph  12. 


j86  STEAM-BOILERS. 

Test-pieces  and  Methods  of  Testing. 

8.  Test  Specimen  for  Tensile  Test. — The  standard  test  speci- 
men of  eight  inch  (8")  gauged  length  shall  be  used  to  determine 
the  physical  properties  specified  in  paragraphs  Xos.  4  and  5. 

For  other  material  the  test  specimen  may  be  the  same  as  for 
sheared  plates,  or  it  may  be  planed  or  turned  parallel  throughout 
its  entire  length;  and  in  all  cases,  where  possible,  two  opposite 
sides  of  the  test  specimens  shall  be  the  rolled  surfaces.  Rivet 
rounds  and  small  rolled  bars  shall  be  tested  of  full  size  as  rolled. 

9.  Number  of  Tensile  Tests. — One  tensile  test  specimen  will 
be  furnished  from  each  plate  as  it  is  rolled,  and  two  tensile  test 
specimens  will  be  furnished  from  each  melt  of  rivet  rounds.  In 
case  any  one  of  these  develops  flaws  or  breaks  outside  of  the 
middle  third  of  its  gauged  length,  it  may  be  discarded  and  another 
test  specimen  substituted  therefor. 

10.  Test  Specimens  for  Bending. — For  material  three-fourths 
inch  (3/4")  or  less  in  thickness  the  bending  test  specimen  shall 
have  the  natural  rolled  surface  on  two  opposite  sides.  The 
bending  test  specimens  cut  from  plates  shall  be  one  and  one-half 
inches  (iV')  wide,  and  for  material  more  than  three-fourths  inch 
(5  4")  thick  the  bending  test  specimen  may  be  one-half  inch  (1/2") 
thick.  The  sheared  edges  of  bending  test  specimens  may  be 
milled  or  planed.  The  bending  test  specimens  for  rivet  rounds 
shall  be  of  full  size  as  rolled.  The  bending  test  may  be  made  by 
pressure  or  by  blows. 

11.  Number  of  Bending  Tests. — One  cold  bending  specimen 
and  one  quenched  bending  specimen  will  be  furnished  from  each 
plate  as  it  is  rolled.  Two  cold  bending  specimens  and  two 
quenched  bending  specimens  will  be  furnished  from  each  melt 
of  rivet  rounds.  The  homogeneity  test  for  fire-box  steel  shall 
be  made  on  one  of  the  broken  tensile  test  specimens. 

12.  Homogeneity  Tests  for  Fire-box  Steel. — The  homogeneity 
test  for  fire-box  steel  is  made  as  follows:  A  portion  of  the  broken 
tensile  test  specimen  is  either  nicked  with  a  chisel  or  grooved  on 


STREXCTH     OF    BOILERS.  i%j 

a  machine,  transversely  about  a  sixteenth  of  an  inch  (1/16") 
deep,  in  three  places  about  two  inches  (2")  apart.  The  first  groove 
should  be  made  on  one  side,  two  inches  (2")  from  the  square 
end  of  the  specimen;  the  second,  two  inches  (2")  from  it  on  the 
opposite  side;  and  the  third,  two  inches  (2")  from  the  last,  and 
on  the  opposite  side  from  it.  The  test  specimen  is  then  put  in  a 
vise,  with  the  first  groove  about  a  quarter  of  an  inch  (1/4")  above 
the  jaws,  care  being  taken  to  hold  it  firmly.  The  projecting  end 
of  the  test  specimen  is  then  broken  off  by  means  of  a  hammer, 
a  number  of  light  blows  being  used,  and  the  bending  being  away 
from  the  groove.  The  specimen  is  broken  at  the  other  two  grooves 
in  the  same  way.  The  object  of  this  treatment  is  to  open  and 
render  visible  to  the  eye  any  seams  due  to  failure  to  weld  up, 
or  to  foreign  interposed  matter  or  cavities  due  to  gas  bubbles  in 
the  ingot.  After  rupture,  one  side  of  each  fracture  is  examined, 
a  pocket  lens  being  used,  if  necessary,  and  the  length  of  the 
seams  and  cavities  is  determined. 

13.  Yield- point. — For  the  purpose  of  this  specification  the 
yield-point  shall  be  determined  by  the  careful  observation  of  the 
drop  of  the  beam  or  halt  in  the  gauge  of  the  testing-machine. 

14.  Sample  for  Chemical  Analysis. — In  order  to  determine  if 
the  material  conforms  to  the  chemical  limitations  prescribed  in 
paragraph  2  herein,  analysis  shall  be  made  of  drillings  taken  from 
a  small  test  ingot.  An  additional  check  analysis  may  be  made 
from  a  tensile  specimen  of  each  melt  used  on  an  order,  other  than 
in  locomotive  fire-box  steel.  In  the  case  of  locomotive  fire-box 
steel  a  check  analysis  may  be  made  from  the  tensile  specimen 
from  each  plate  as  rolled. 

Variation  ix  Weight. 

15.  The  variation  in  cross-section  or  weight  of  more  than 
2 J  per  cent  from  that  specified  will  be  sufficient  cause  for  rejection, 
except  in  the  case  of  sheared  plates,  which  will  be  covered  by  the 
following  permissible  variations: 


i88 


STEAM-BOILERS. 


(e)  Plates  i2i  pounds  per  square  foot  or  heavier,  up  to  ioo 
inches  wide,  when  ordered  to  weight,  shall  not  average  more 
than  2 \  per  cent  variation  above  or  2\  per  cent  below  the  theo- 
retical weight.  When  ioo  inches  wide  and  over,  5  per  cent  above 
or  5  per  cent  below  the  theoretical  weight. 

(/)  Plates  under  \2\  pounds  per  square  foot,  when  ordered 
to  weight,  shall  not  average  a  greater  variation  than  the  following : 

Up  to  75  inches  wide,  2'  per  cent  above  or  2§  per  cent  below 
the  theoretical  weight.  75  inches  wide  up  to  100  inches  wide, 
5  per  cent  above  or  3  per  cent  below  the  theoretical  weight. 
When  100  inches  wide  and  Over,  10  per  cent  above  or  3  per  cent 
below  the  theoretical  weight. 

(g)  For  all  plates  ordered  to  gauge,  there  will  be  permitted  an 
average  excess  of  weight  over  that  corresponding  to  the  dimen- 
sions on  the  order,  equal  in  amount  to  that  specified  in  the  follow- 
ing table : 


Table  of  Allowances  for  Overweight  for  Rectangular 
Plates  when  Ordered  to  Gauge. 

Plates  will  be  considered  up  to  gauge  if  measuring  not  over 
1  /ioo  inch  less  than  the  ordered  gauge. 

The  weight  of  1  cubic  inch  of  rolled  steel  is  assumed  to  be 
0.2833  pound. 

PLATES  1/4  INCH  AND  OVER  IN  THICKNESS. 


Width  of  Plate. 

Thickness  of  Plate 

Inch. 

Up  to  75  Inches. 

75  to  100  Inches. 

Over  100  Inches. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

1/4 

10 

14 

18 

5/16 

8 

12 

16 

3/8 

7 

10 

13 

7/16 

6 

8 

10 

1/2 

5 

7 

9 

9/16 

4* 

6£ 

8* 

5/8 

•4 

6 

8 

Over   5/8 

3* 

5 

6J 

STRENGTH    OF    BOILERS. 
PLATES  UNDER  1/4  INCH  IN  THICKNESS. 


189 


Thickness  of  Plate. 
Inch. 

Width  of  Plate. 

Up  to  50   Inches.       f>0  Inches  and  Above. 
Per  Cent.                          Per  Cent. 

1/8  up  to  5/32 
5/32  up  to  3/16 
3/16  up  to   1/4 

10 
8§ 

7 

15 

IO 

Finish. 

16.  All  finished  material  shall  be  free  from  injurious  surface 
defects  and  laminations,  and  must  have  a  workmanlike  finish. 


Branding. 

17.  Every  finished  piece  of  steel  shall  be  stamped  with  the 
melt  number,  and  each  plate  and  the  coupon  or  test  specimen 
cut  from  it  shall  be  stamped  with  a  separate  identifying  mark  or 
number.  Rivet  steel  may  be  shipped  in  bundles  securely  wired 
together  with  the  melt  number  on  a  metal  tag  attached. 

Inspection. 

18.  The  inspector,  representing  the  purchaser,  shall  have  all 
reasonable  facilities  afforded  to  him  by  the  manufacturer  to 
satisfy  him  that  the  finished  material  is  furnished  in  accordance 
with  these  specifications.  All  tests  and  inspections  shall  be  made 
at  the  place  of  manufacture  prior  to  shipment. 

Laminations. — The  upper  end  of  the  ingot  into  which  the 
molten  steel  from  the  open-hearth  furnace  is  cast,  is  liable  to  be 
affected  by  bubbles  and  other  imperfections  when  the  ingot  is 
poured  from  the  top.  Such  imperfections,  if  they  are  not  re- 
moved, give  rise  to  lamination  in  the  plates,  and  therefore  when 
the  ingot  is  rolled  into  blooms  the  crop  end  should  be  cut  long 
enough  to  remove  all  the  bubbles.  There  is  always  a  tendency, 
on  account  of  the  reduction  of  prices  through  competition,  to 


ioo 


STEAM-BOILERS. 


reduce  the  length  of  the  crop  end,  and  consequently  steel  plates, 
though  having  the  other  required  physical  properties,  are  liable 
to  show  lamination. 

It  is  to  be  noted  that  fire-box  steel  is  better  than  flange  steel. 

Blue  Heat. — Steel  plates,  and  other  forms  of  mild  steel, 
become  brittle  at  a  temperature  corresponding,  roughly,  to  a 
blue  heat.  A  plate  that  will  endure  bending  double,  both 
hot  and  cold,  is  liable  to  show  cracks  if  bent  at  a  blue  heat. 
In  bending,  flanging,  and  forging  no  work  should  be  done  on 
steel  at  a  blue  heat ;  properly,  such  work  should  be  done  at 
a  bright  red  heat;  work  should  never  be  continued  after  the 
steel  becomes  black.  After  the  steel  is  cold  it  may  be  bent 
as  readily  as  iron  at  the  same  temperature. 

Wrought  Iron — All  the  stays  and  fastenings  of  boilers 
that  are  made  by  welding  should  be  made  of  tough,  ductile 
wrought  iron.  Welds  made  by  a  skilful  smith  may  have  as 
great  a  strength  as  the  bar  from  which  they  are  made.  A 
ductile  bar  may  break  in  the  clear  bar  instead  of  in  the  weld, 
on  account  of  the  hardening  due  to  the  work  done  on  the  bar 
at  the  weld.  It  is  customary  to  assume  that  25  to  50  per 
cent  of  the  strength  of  the  bar  may  be  lost  by  welding. 

Wrought-iron  plates  of  a  quality  suitable  for  boiler-making 
are  now  more  expensive  than  mild-steel  plates,  which  are  in 
every  way  as  well  adapted  to  the  purpose,  and  which  have  a 
higher  strength.  Consequently  we  find  wrought-iron  plates 
used  only  when  specially  demanded.  Wrought  iron  does  not 
show  cracks  when  worked  at  a  blue  heat,  and  in  general  may 
endure  more  abuse  in  working.  This  caused  wrought  iron 
to  be  preferred  by  many  after  reliable  steel  was  produced 
cheaply,  but  boiler- makers  now  understand  the  working  of 
steel  plates  and  avoid  improper  handling. 

Wrought-iron  plates  should  show  a  limit  of  elasticity  of 
23,000  pounds,  and  a  tensile  strength  of  45,000  pounds  to 
the  square  inch. 


STREXGTII  OF  BOILERS. 


191 


Wrought-iron  rods  and  bolts  should  have  a  strength  of 
48,000  pounds  per  square  inch. 

Rivets. — The  rivets  used  in  boiler-making  are  either  iron, 
or  steel  similar  in  quality  to  steel  used  for  boiler-plates. 

A  rivet  should  bend  cold  around  a  bar  of  the  same 
diameter,  and  it  should  bend  double  when  hot  without  frac- 
ture. The  tail  should  admit  of  being  hammered  down  when 
hot  till  it  forms  a  disk  2\  times  the  diameter  of  the  shank, 
without  cracking.  The  shank  should  admit  of  being  ham- 
mered flat  when  cold,  and  then  punched  with  a  hole  equal  in 
diameter  to  that  of  the  shank,  without  cracking. 

The  rods  from  which  rivets  are  made  should  show  a  tensile 
strength  of  about  55,000  pounds  for  steel  and  about  48,000 
pounds  for  wrought  iron.  The  other  properties,  such  as 
ultimate  elongation  and  contraction  of  area,  should  be  like 
those  for  boiler-plate. 

The  shearing  strength  of  steel  rivets  is  about  45,000 
pounds,  and  of  iron  rivets  about  38,000  pounds;  that  is,  the 
shearing  strength  will  be  between  ,TII  and  1%  of  the  tensile 
strength. 

Cast  Iron  in  different  forms  will  show  a  tensile  strength 
of  12,000  to  20,000  pounds  to  the  square  inch.  Gun-iron, 
which  is  cast  iron  made  with  special  care  and  skill  from 
selected  stock,  has  shown  a  tensile  strength  of  nearly  30,000 
pounds  to  the  square  inch.  In  compression  the  strength  of 
small  pieces  may  be  as  high  as  80,000  pounds  to  the  square 
inch,  but  larger  pieces,  like  columns,  fail  at  30,000  pounds 
to  the  square  inch. 

Cast  iron  is  used  for  some  or  all  of  the  parts  of  sectional 
boilers,  and  for  fittings  such  as  manholes,  though  wrought 
iron  is  preferable  for  such  purposes.  Flat  plates  at  the  ends 
of  cylindrical  boilers  are  sometimes  made  of  cast  iron. 

In  general,  cast  iron  should  never  be  used  when  it  is  sub- 
jected to  severe  changes  of  temperature  or  to  stresses  from 


192  STEAM-BOILERS. 

unequal  expansion,  and  should  be  replaced  by  wrought  iron 
or  mild  steel  whenever  it  is  practicable. 

Couplings,  elbows,  and  other  pipe-fittings  are  made  of 
cast  iron.  The  brittleness  is  a  convenience  when  changes  are 
to  be  made,  as  joints  that  cannot  be  opened  are  readily 
broken. 

Malleable  Iron,  which  is  cast  iron  toughened  by  being 
deprived  of  part  of  the  carbon,  is  used  for  pipe-fittings  and  for 
fittings  of  steam-boilers.  It  is  used  in  place  of  cast  iron  for 
sectional  boilers  and  for  parts  of  water-tube  boilers.  Though 
tougher  than  cast  iron,  and  though  it  will  endure  forging  to 
some  extent,  its  variability  in  quality  and  its  unreliability 
prevent  much  reduction  in  weight  and  size  when  substituted 
for  cast  iron. 

Copper  is  largely  used  in  Europe  for  making  fire-boxes  of 
locomotive-boilers  and  torpedo-boat  boilers.  Its  greater  cost 
is  in  part  offset  by  the  value  of  the  scrap  copper  after  the 
fire-box  is  worn  out. 

Copper  for  fire-boxes,  rivets,  and  stays  should  have  a  ten- 
sile strength  of  34,000  pounds  to  the  square  inch,  and  should 
show  an  elongation  of  20  to  25  per  cent  in  8  inches.  It  should 
not  contain  more  than  one-half  per  cent  of  impurities.  The 
greater  ductility  of  copper,  and  its  greater  thermal  conduc- 
tivity, permitting  of  greater  thickness  for  furnace-plates, 
recommends  it  to  European  engineers. 

Copper  is  largely  used  on  steamships  for  making  piping  of 
all  sorts,  such  as  steam-pipes  and  water-pipes.  Such  pipes 
are  made  of  sheet  copper,  rolled  up  or  hammered  to  shape, 
scarfed  and  brazed  at  the  edges.  The  pipe  is  also  brazed  to 
brass  flanges  for  coupling  lengths  of  pipe,  or  for  joining  to 
steam-chests  or  other  parts  of  the  engine  or  boiler.  If  the 
brazing  is  not  done  with  care  and  skill  the  brazed  joint  may 
lose  as  much  as  half  the  strength  of  the  sheet  copper.  Several 
disastrous  explosions  of  such  piping  have  occurred.      Conse- 


STRENGTH  OF  BOILERS.  1 93 

quently  wrought-iron  piping  is  finding  favor  for  high  pressure 
steam. 

Bronze  and  Composition.  Brass. — Bronze  is  properly 
an  alloy  of  copper  and  tin;  thus  gun-metal  is  90  parts  of 
copper  to  10  of  tin.  Compositions  of  various  qualities  are 
made  of  copper  and  zinc  with  more  or  less  tin.  Brass  is  an 
alloy  of  copper  and  zinc;  for  example,  brass  smoke-tubes  are 
made  of  70  parts  of  copper  to  30  parts  of  zinc.  Lead  is 
added  to  brass  and  to  composition  to  reduce  the  cost  and  to 
make  the  metal  work  easier.  It  may  be  considered  as  an 
adulteration,  as  it  cheapens  the  metal  at  the  expense  of  the 
quality.  There  are  many  special  bronzes,  such  as  phosphor- 
bronze  and  aluminium-bronze,  which  are  used  for  special 
purposes. 

Brass  is  used  to  some  extent  for  smoke-tubes  of  locomo- 
tive and  other  boilers,  on  account  of  its  greater  thermal  con- 
ductivity, by  European  engineers.  In  America,  brass  is  used 
for  valves,  gauges,  and  other  boiler  fittings.  Composition  or 
bronze  is  advantageously  used  for  the  valves  and  seats  of 
safety-valves  and  wherever  the  service  endured  is  excep- 
tionally hard.  Brass  is  more  commonly  used  because  it  is 
cheaper.  In  a  general  way  it  may  be  said  that  the  cost  and 
quality  of  brass  and  composition  is  proportional  to  the  copper 
it  contains;  thus  red  brass  is  better  and  costs  more  than 
yellow  brass.  Many  small  brass  fittings  on  the  market  are 
sold  at  a  price  which  precludes  the  use  of  proper  alloys,  and 
they  are  consequently  soft  and  worthless. 

Stay-bolts  are  usually  arranged  in  equidistant  horizontal 
and  vertical  rows;  as  an  example  we  may  take  the  stay-bolts 
in  the  locomotive  fire-box  on  Plate  II.  These  bolts  are  7/8 
of  an  inch  in  diameter  outside  of  the  threads,  and  are  spaced 
4  inches  on  centres.  The  total  load  on  each  stay-bolt  with 
a  steam-pressure  of  170  pounds  to  the  square  inch  is 

4  X  4  X  170  =  2720  pounds. 


194 


STEAM-BOILERS. 


The  diameter  of  the  bolt  at  the  bottom  of  the  screw-thread 
is  about  0.7  of  an  inch,  and  the  area  of  the  section  is  about 
0.4  of  a  square  inch.      The  stress  is  consequently 

2720  -i-  0.4  =  6800. 

Sometimes  the  area  is  calculated  from  the  external  diam- 
eter of  the  bolt,  a  proceeding  which  may  lead  to  a  gross  error. 
In  the  present  instance  the  corresponding  area  is  about  0.6 
of  a  square  inch,  which  gives  an  apparent  stress  of  about 
4500. 

Suppose  that  the  thread  is  turned  off  from  the  body  of 
the  bolt,  and  that  the  diameter  is  thereby  reduced  to  5/8  of 
an  inch.  The  area  of  the  section  is  then  about  0.3  of  an 
inch,  and  the  stress  is 

2720  -h  0.3  =  9000  -j-. 

The  stress  on  stay-bolts  should  always  be  low  to  allow 
for  wasting  from  corrosion,  and  to  allow  for  unknown  addi- 
tional stresses  that  may  be  caused  by  the  unequal  expansion 
of  the  plates  that  are  tied  together  by  the  stay-bolts. 

Stay-rods. — Through-stays  like  those  passing  through  the 
steam-space  of  the  marine  boiler,  shown  by  Fig.  11,  page  17, 
are  treated  much  like  stay-bolts.  Thus  the  stays  in  question 
are  14  inches  apart  horizontally  and  13  inches  apart  vertically. 
If  they  are  each  assumed  to  support  a  rectangular  area  13 
inches  wide  and  14  inches  long,  the  total  force  from  160 
pounds  steam-pressure  will  be 

14  X  13  X  160  =  29120. 

The  diameter  of  these  stays  in  the  body  is  2  inches,  which 
gives  an  area  of  section  of  3.14  square  inches.     The  stress  is 

consequently 

29120  -4-3.14  =  9300 


STRENGTH  OF  BOILERS. 


!95 


These  stay-rods  have  swaged  heads  on  which  the  screw- 
thread  is  cut,  so  that  the  diameter  at  the  bottom  of  the 
thread  is  greater  than  the  diameter  of  the  body. 

Stay-rods  which  are  used  in  connection  with  girders,  as  on 
Plate  I,  will  have  to  carry  loads  which  depend  on  the  surface 
supported,  the  steam-pressure,  and  the  number  and  arrange- 
ment of  the  stays.  The  determination  of  the  load  may  be 
difficult  and  uncertain,  but  the  calculation  of  the  stress  for  a 
given  load  is  very  simple. 

Diagonal  Stays. — If  a  stay-rod  runs  diagonally  from  a 
flat  plate  to  the  shell  of  a  boiler,  it  will  evidently  be  subjected 


Fig.  86. 
to  a  greater  stress  than  it  would  be  if  it  were  a  through-stay. 
Thus  in  Fig.  86  we  have  at  the  point  a  the  parallelogram  of 
forces  abed;  ab  is  the  total  pressure  supported  by  the  stay,  ac 
is  the  pull  on  the  stay,  and  ad  is  a  force  that  must  be  taken 
up  by  the  flat  plate.  But  the  triangles  abc  and  acf  are  simi- 
lar, so  that  we  have 


ac 

ab 


S 


ae  -f-  ef 


Suppose,  for  example,  that  ac  is  two  feet  and  ef  is  six 
feet;  then 


ac         V21  +  62 
ab  =         6 


=  1.054, 


196 


STEAM-BOILERS. 


or  the  pull  on  the  stay  is  more  than  five  per  cent  in  excess  of 
what  a  through-stay  would  be  required  to  support. 

Gusset-stays  are  open  to  the  defect  that  the  distribu- 
tion of  stress  on  the  plate  forming  the  stay  is  uneven  and 
uncertain.  It  is  customary  to  calculate  them  on  the  assump- 
tion that  the  resultant  stress  acts  along 
a  medial  line,  and  is  evenly  distributed 
over  a  section  at  right  angles  to  that  line. 
A  low  apparent  working-stress  should  be 
used. 

Thin    Hollow  Cylinder.  —  Let   Fig. 
87    represent    a    semicircular  steam-drum 
closed  at  the  bottom  by  a  thick  flat  plate. 
If  the  steam-pressure  is  p  pounds  per  square  inch,  the  radius 
is  r,  and  the  length  is  /,  then  the  pressure  on  the  plate  is 

2prl. 

If  the  thickness  of  the  cylinder  is  /,  and  the  stress  per 
square  inch  on  the  metal  of  the  cylinder  is  s,  then  the  pull  of 
the  cylinder  at  one  end  of  the  plate  is 

stl. 


Fig.  87. 


But  this  must  be  equal  to  half  the  pressure  on  the  plate, 
so  that 

stl  =  prl. 


s  = 


pr 


For  safety  the  stress  should  not  exceed  the  safe  working 
stress  for  the  material  of  which  the  cylinder  is  made ;  so  that 
we  have 


STRENGTH  OF  BOILERS.  1 97 

It  is  evident  that  the  pull  on  the  side  of  the  cylinder  and 
the  stress  per  square  inch  will  be  the  same  if  another  half- 
cylinder  is  substituted  for  this  plate,  making  a  complete  thin 
hollow  cylinder. 

Example  1. — A  thin  hollow  cylinder  five  feet  in  diameter 
and  half  an  inch  thick,  working  at  a  pressure  of  200  pounds, 
will  be  subjected  to  a  stress  of 

5  X   12 

200  x '-  i  =  12,000 

pounds  per  square  inch.  If  the  cylinder  is  made  of  one  con- 
tinuous plate  of  steel  without  longitudinal  joint,  this  stress 
will  be  about  one  fifth  of  the  ultimate  strength. 

Example  2. — If  it  is  desired  that  the  stress  shall  be  9000 
pounds  in  a  cylinder  9  feet  in  diameter  when  exposed  to  a 
pressure  of  120  pounds  to  the  square  inch,  then  the  thickness 
of  the  plate  should  be 

pr                    9  X    12 
t  —  —  =  120  X  -£-  9000  =  0.72 

of  an  inch. 

End  Tension  on  a  Cylinder. — In  the  preceding  cylinder 
we  have  considered  the  tension  on  a  section  at  the  side  of  the 
cylinder.  Let  us  now  consider  the  tension  on  a  transverse 
section. 

If  the  cylinder  is  closed  by  a  flat  plate  at  the  end,  the 
area  of  that  plate  will  be 

3.1416*-*, 

and  the  total  force  due  to  a  pressure  of  p  pounds  per  square 
inch  will  be 

3.i4i6r>. 


198  STEAM-BOILERS. 

This  force  will  be  resisted  by  a  ring  of  metal  having  a  cir- 
cumference 2  X  3.14167-,  and  a  thickness  /.  The  resistance 
of  the  ring  will  be 

2  X  3.1416/-/*, 

representing  the  stress  by  s.      Consequently  we  shall  have 
2  X  3. 14167*/*  =  3.1416/**/. 

2/ 

It  is  evident  that  the  stress  from  the  end  pull  is  half  the 
stress  on  the  section  at  the  side  of  a  cylinder,  and  conse- 
quently a  cylinder  made  of  homogeneous  material  without 
joints  will  always  be  ruptured  longitudinally. 

It  is  also  evident  that  the  stress  from  the  end  pull  will  be 
the  same  if  the  end  of  the  cylinder  is  closed  by  a  spherical 
surface,  or  by  any  other  figure,  instead  of  a  flat  plate. 

Thin  Hollow  Sphere- — A  section  taken  through  the  cen- 
tre of  a  sphere  is  in  the  same  condition  as  a  transverse  sec- 
tion of  a  thin  cylinder,  and  will  be  subjected  to  the  same 
stress,  if  the  sphere  has  the  same  thickness  and  is  subjected 
to  the  same  internal  pressure. 

Formerly  the  ends  of  plain  cylindrical  boilers  were  made 
hemispherical,  but  such  ends  are  difficult  to  make  and  are 
needlessly  strong  if  of  the  same  thickness  as  the  cylindrical 
shell.  It  is  now  the  practice  to  curve  such  ends  to  a  less 
radius  than  that  of  the  cylindrical  shell.  If  the  radius  of  the 
head  is  equal  to  the  diameter  of  the  shell,  then  with  the  same 
thickness  of  plate  the  stress  will  be  the  same  per  square  inch, 
provided  there  are  no  seams  in  head  or  shell.  The  heads 
usually  do  not  have  a  seam,  and  the  shells  always  have  a 
seam ;  the  margin  of  strength  in  the  head,  when  the  same 
thickness  of  plate  is  used,  under  this  condition  may  be  offset 
against  the  possible  injury  done  to  the  head  in  shaping  it. 


STRENGTH  OF  BOILERS.  199 

The  construction  known  as  a  bumped-up  head  has  the 
edge  flanged  into  a  cylindrical  form  to  make  a  joint  with  the 
shell,  and  to  avoid  the  awkward  stress  that  would  be  thrown 
onto  the  cylindrical  shell  if  the  true  cylindrical  and  spherical 
surfaces  were  allowed  to  intersect. 

If  it  is  inconvenient  to  curve  the  head  to  a  radius  as  small 

as  the  diameter  of  the  cylinder,  then  a  thicker 

f> — b—^T    plate  may  be  used,  with  a  longer  radius. 

f' .  A.  ■  '  .'H  Rivets. — The  plates  of  a  boiler  are  joined  at 

the  edges  by  rivets;   rivets  are  also  used  in  stays 

and  other  members. 

The  usual  form  of  rivets  is  shown  by  Fig. 
88.  If  the  diameter  of  the  rivet  is  D,  then  the 
proportions  may  be 


D~ 

1.4; 

B 
D~ 

1.2; 

C 
D~ 

0.7; 

b 
D~ 

3/4- 

The  length  of  the  rivet  will  depend  on  the  number  and 
thickness  of  the  plates  through  which  it  is  to  pass. 

The  rivet  represented  by  Fig.  88  has  a  pan  head.  Of  the 
rivets  shown  by  Fig.  89,  A,  B,  and  C  have  pan  heads,  and  D 
and  E  have  round  or  hemispherical  heads. 

The  form  of  the  point  of  a  rivet  will  depend  on  the  way 
in  which  the  rivet  is  driven  and  on  the  shape  of  the  tools  or 
dies  used  for  forming  the  point.      The  rivet  A  has  a  straight 


200 


STEAM-BOILERS. 


conical  point ;  this  is  the  only  form  that  can  be  made  when 
the  rivet  is  driven  by  hand  with  flat-faced  hammers. 

The  rivet  B  has  the  head  formed  by  a  die  or  snap.  The 
rivet  is  driven  by  a  few  heavy  blows  of  a  hammer,  and  the 
head  is  roughly  formed ;  then  a  die  or  snap  is  placed  on  the 
point  and  driven  to  form  the  point  by  a  sledge-hammer. 

C  shows  a  rounded  conical  point  commonly  used  for 
machine-driven  rivets.  The  heads  of  such  rivets  may  have  a 
similar  form. 

D  represents  the  usual  form  of  countersunk  rivets:  the 
hemispherical  head  is  not  a  peculiarity  of  such  rivets;  it  is 


occasionally  used  with  any  form  of  point.  The  rivet  E  has 
some  fulness  or  projection  at  the  point  beyond  the  counter- 
sink. 

After  a  rivet  is  driven,  both  ends  are  called  heads;  the 
distinction  of  heads  and  points  is  made  here  for  convenience 
in  description. 

The  straight  conical  form  A  is  liable  to  be  too  flat  and 
weak.  Its  height  should  be  three-fourths  the  diameter  of 
the  rivet. 

When  rivet-holes  are  punched  in  plates  they  are  slightly 
conical,  as  shown  by  B,  Fig.  89,  which  shows  the  two  smaller 
ends  of  the  rivet-holes  placed  together  to  facilitate  the  proper 
filling  of  the  hole  by  the  rivets.  The  other  rivet-holes  are 
straight,  as  they  would  be  if  drilled. 


STRENGTH    OF     BOILERS.  201 

Riveted  Joints. — The  proportions  of  riveted  joints,  such 
as  diameter  and  pitch  of  rivets,  are  determined  in  part  by 
practice  and  in  part  by  a  method  of  calculation  to  be  explained 
later.  In  practice  it  is  found  necessary  to  limit  the  pitch  of 
the  rivets,  and  consequently  the  diameter,  to  be  used  with  a 
given  thickness  of  plate,  in  order  that  the  joint  may  be  made 
tight  by  calking.  This  limitation  frequently' makes  the  joint 
weaker  than  it  otherwise  would  be. 

The  edges  of  plates  are  either  lapped  over  and  rivetec',  or 
brought  edge  to  edge  and  then  joined  by  a  cover-plate  which 
is  riveted  to  each  of  the  two  plates.  The  first  method  makes 
a  lap-joint  and  the  second  a  butt-joint. 

Fig.  90  shows  a  single-riveted  lap-joint  and  Figs.  91  and  02 
show  double  riveted  lap-joints.  The  rivets  in  Fig.  91  are  said 
to  be  staggered;  the  form  shown  by  Fig.  92  is  called  chain-rivet- 
ing. 

Butt-joints  with  two  cover-plates  are  shown  by  Figs.  95,  96, 
and  97.  The  outer  cover-plate  is  narrow,  with  rivets  placed  close 
enough  together  to  provide  for  sound  calking.  The  inner  plate 
is  wider,  and  as  its  edges  are  not  calked  they  may  have  a  row  of 
more  widely  spaced  rivets.  These  joints,  and  those  shown  by 
Figs.  93  and  94,  are  designed  with  the  view  of  securing  more 
strength  than  can  be  had  with  a  plain  lap-joint  like  Fig.  91,  or 
than  can  be  had  with  a  butt-joint  with  cover-plates  of  equal 
width. 

Efficiency  of  a  Riveted  Joint. — The  strength  of  a  riveted 
joint  is  always  less  than  that  of  the  solid  plate,  because  some  of 
the  plate  is  cut  away  by  the  rivets.  This  is  very  evident  in  the 
case  of  a  single-riveted  joint,  such  as  that  shown  by  Fig.  90;  it 
will  be  found  to .  be  true  for  more  complicated  joints,  such 
as  those  shown  by  Figs.  95,  96,  and  97.  The  efficiency 
of  a  riveted  joint  is  the  ratio  of  the  strength  of  the  joint  to  the 
stength  of  the  solid  plate. 

The   strength  and  efficiency  of  a  given  riveted  joint  can  be 


202  STEAM-BOILERS. 

properly  determined  only  by  direct  test  on  full-sized  speci- 
mens, which  have  considerable  width.  Tests  on  narrow 
specimens  are  liable  to  be  misleading.  Tests  on  boiler-joints 
are  expensive,  and  can  be  made  only  on  large  and  power- 
ful testing-machines.  Tests  have  been  made  on  behalf  of 
the  United  States  Navy  Department  at  the  Watertown 
Arsenal  on  a  large  number  of  single-riveted  joints,  on  a  con- 
siderable number  of  double-riveted  joints,  and  on  a  few 
special  joints.  A  few  tests  have  been  made  elsewhere  on  full- 
sized  joints.  These  tests  give  us  important  information  that 
can  be  used  in  designing  joints  for  boilers,  but  we  cannot  in 
general  select  a  joint  directly  from  the  tests. 

Methods  of  Failure.— A  riveted  joint  may  fail  in  one  of 
several  methods,  depending  on  the  proportions,  such  as  thick- 
ness of  plate  and  the  diameter  and  pitch  of  the  rivets.  This 
can  be  clearly  seen  in  case  of  a  single-riveted  joint  like  that 
shown  by  Fig.  90.      Such  a  joint  may  fail: 

(1)  By  tearing  the  plate  at  the  reduced  section  between  the 
rivets.  If  the  rivets  have  the  diameter  d  and  the  pitch  pt 
then  the  ratio  of  the  area  of  the  reduced  section  to  that  of 
the  whole  plate  is 


P 


P 


(2)  By  shearing  the  rivets. 

(3)  By  crushing  the  plate  or  the  rivets  at  the  surface  where 
they  are  in  contact. 

(4)  By  cracking  the  plate  between  the  rivet-hole  and  the 
edge  of  the  plate,  or  by  some  method  of  failure  due  to  in- 
sufficient lap.  A  riveted  joint  never  fails  by  this  method  in 
practice,  because  the  lap  can  always  be  made  sufficient. 

The  failure  of  more  complicated  joints  may  occur  in 
various  methods,  which  will  be  considered  fn  connection  with 
the  calculation  of  some  special  joints. 


STRENGTH    OF    BOILERS.  2C^ 

Drilled  or  Punched  Plates. — In  the  better  class  of  boiler- 
shops  it  is  now  the  practice  to  drill  rivet-holes  in  plates  after 
the  plates  are  in  place,  so  that  the  holes  are  sure  to  be  fair. 
Sometimes  the  holes  are  punched  to  a  smaller  diameter  and 
then  drilled  out  to  the  final  size  after  the  plates  are  in  place. 
The  result  is  the  same  as  though  the  holes  were  drilled  in  the 
first  place,  as  the  metal  near  the  hole,  which  was  injured  in 
punching,  is  all  removed.  The  metal  remaining  between 
drilled  holes  does  not  have  its  properties  changed  by  the 
drilling.  On  the  contrary,  the  metal  between  punched  holes 
is  always  injured  more  or  less.  In  general,  soft  ductile  metal 
is  injured  less  than  hard  metal,  and  further,  soft-steel  plates 
are  injured  less  than  wrought-iron  plates. 

When  boiler-plates  are  punched  and  then  rolled  to  form 
cylindrical  shells,  some  of  the  holes  are  liable  to  come  unfair, 
so  that  a  rivet  cannot  be  passed  through.  In  such  cases  the 
holes  should  be  drilled  to  a  larger  size,  and  a  rivet  of  corre- 
sponding diameter  should  be  substituted.  Careless  or  reck- 
less workmen  sometimes  drive  in  a  drift-pin,  and  stretch  or 
distort  the  unfair  holes  so  that  a  rivet  can  be  forced  through. 
The  plate  is  liable  to  be  severely  injured  by  such  treatment, 
and  the  rivet  cannot  properly  fill  the  rivet-holes.  Unfortu- 
nately it  is  difficult  or  impossible  to  detect  bad  work  of  this 
kind  after  the  rivets  are  driven. 

Tearing. — The  metal  between  the  rivet-holes  in  a  riveted 
joint  cannot  stretch  as  a  proper  test-piece  does  in  the  testing- 
machine,  and  consequently  it  shows  a  greater  tensile  strength 
than  a  test-piece  from  the  same  plate.  Some  tests  on  single 
or  double  riveted  joints  with  small  pitches  show  an  excess 
of  strength  from  this  cause,  amounting  to  ten  per  cent  or 
more.  The  excess  appears  to  be  uncertain  and  irregular,  so 
that  if  any  allowance  is  made  for  it,  it  should  be  by  a  skilled 
designer  after  a  careful  study  of  all  .the  tests  that  have  been 
made.  Ordinarily  it  will  be  safer  to  use  the  tensile  strength 
shown  by  test-pieces  in  the  testing-machine,  especially  for  joints 
like   Fig.  93;  which  have  a  large  pitch  for  some  of  the  rivets. 


204  STEAM-BOILERS. 

Shearing1. — In  general  it  is  fair  to  assume  the  shearing 
strength  of  rivets  of  iron  or  steel  to  be  between  TV  and  1%  of  the 
tensile  strength  of  the  metal  from  which  the  rivets  are  made. 

Crushing. — It  is  customary  to  assume  that  the  pull  on  a 
riveted  joint  is  evenly  distributed  among  the  rivets  in  the 
joint,  and  to  divide  the  total  pull  by  the  number  of  rivets  to 
find  the  shearing  or  crushing  force  acting  on  one  rivet.  It  is 
further  customary  to  assume  that  the  intensity  of  the  crushing 
force  on  the  surface  where  the  rivet  bears  on  the  plate,  may 
be  found  by  dividing  the  total  force  on  one  rivet,  by  the 
product  of  the  diameter  of  a  rivet  and  the  thickness  of  the 
plate. 

The  crushing-stress  on  rivets  in  joints  that  fail  by  crushing 
is  found  by  experiment  to  be  high  and  irregular.  In  some 
cases  it  has  amounted  to  150,000  pounds  per  square  inch;  in 
a  few  tests  it  is  less  than  85,000  pounds.  It  is  probable  that 
95,000  pounds  may  be  used  with  safety  in  calculating  riveted 
joints  for  boilers.  Now  the  stress  on  the  bearing-surface 
will  seldom  be  so  much  as  one  third  the  ultimate  strength, 
even  during  a  hydraulic  test  of  a  boiler,  and  it  is  not  probable 
that  a  joint  will  be  injured  in  this  way  unless  the  stress 
approaches  the  ultimate  strength. 

Friction  of  Riveted  Joints. — It  is  evident  that  there  must 
be  considerable  friction  between  plates  that  are  firmly  clamped 
together  by  rivets  driven  hot.  It  has  been  proposed  to  take 
some  account  of  this  friction  in  calculating  riveted  joints,  or 
even  to  allow  the  friction  to  be  the  determining  element  in 
proportioning  riveted  joints.  Such  a  method  is  shown  by 
experiment  to  be  unsafe,  for  slipping  takes  place  at  all  loads, 
beginning  at  loads  that  are  much  smaller  than  a  safe  load,  and 
the  effect  of  friction  disappears  before  a  breaking  load  is 
reached. 

Lap. — The  distance  from  the  centre  of  the  rivet-hole  to 
the  edge  of  the  plate  is  called  the  lap.  The  lap  is  usually 
once  and  a  half  the  diameter  of  the  rivet,  a  proportion  that 
appears  to  be  satisfactory. 


STRENGTH  OF  BOILERS.  205 

Diameter  of  Rivet. — The  minimum  diameter  of  punched 
holes  is  determined  by  the  consideration  that  the  punch 
should  not  be  broken.  In  the  ordinary  methods  of  punching 
boiler-plates  the  diameter  of  the  punch  should  at  least  be  as 
much  as  the  thickness  of  the  plate.  It  very  commonly  is 
once  and  a  half  the  thickness  of  the  plate. 

Drilled  rivet-holes  may  have  any  diameter.  They  never 
have  a  diameter  less  than  the  thickness  of  the  plate.  The 
maximum  diameter  of  rivet  to  be  used  with  any  kind  of 
riveted  joint  will  in  general  be  determined  by  the  considera- 
tion that  the  tendency  to  crush  the  plate  in  front  of  the  rivet 
should  not  be  greater  than  the  shearing  strength  of  the  rivet. 
The  maximum  diameter  thus  found  is  liable  to  give  too  large 
a  pitch. 

Pitch. — The  maximum  pitch  for  a  given  plate  along  a 
calked  edge  should  be  determined  by  the  consideration  that 
the  plate  should  be  held  up  rigidly  enough  to  make  a  tight 
joint  without  excessive  calking.  The  pitch  of  rivets,  like 
those  in  the  outer  row  of  the  joint  shown  by  Fig.  78,  need 
not  be  governed  by  this  rule.  There  does  not  appear  to  be 
any  explicit  rule  deduced  either  from  practice  or  experiment 
for  determining  the  proper  pitch  of  rivets. 

Single-riveted  Lap-joint. — In  the  joint  shown  by  Fig.  90 

let  the  thickness  of  the  plate  be  /,  the 

diameter  of  the  rivet  d,  and  the  pitch 
p,  all  in  inches.  Let  the  tearing 
strength  of  the  plate  be  ft=  55,000, 
the  shearing  strength  be  fs  =  45,000, 
and  the  resistance  to  crushing  be 
f.  =  95,000,  all  for  mild  steel. 
Assume  the  proportions 

Fig.  90.  d=I$/l6,      /=7/i6,      p  =  2\ 

It  will  be  sufficient  to  consider  a  portion  of  the  plate 
having  a  width  equal  to  the  pitch.  The  failure  of  such  a  strip 
may  occur  in  one  of  three  ways : 


2o6  STEAM-BOILERS. 

nd2 

1st.   Shearing  one  rivet.     The  area  to  be  sheared  is  

4 

3.1416;/3 
or  : .     The  resistance  to  shearing  is  found  by  multi- 

4  J 

plying  this  area  by  the  shearing  strength  of  the  rivet: 

nd*  n  X  15  X  15  X  45<oorj 

-Vfs  =  -     -43Ti6xT6-        =3>,o63. 

2d.  Tearing  plate  between  rivets.  The  effective  width  of 
the  strip  under  consideration,  allowing  for  the  rivet-hole,  is 
/•  —  d,  and  the  thickness  of  the  plate  is  /,  the  resistance  to 
tearing  is 

(/  -  d)tft  =  {2\  -  |f)TV  X  55-000  =  31,580. 

3d.  Crushing  of  rivet  or  plate.  The  conventional  method 
is  to  assume  the  effective  bearing  area  to  be  equivalent  to  the 
diameter  of  the  rivet  multiplied  by  the  thickness  of  the  plate. 
The  resistance  is  considered  to  be 

dtfc  =  U  X  t\  X  95,ooo  =  38,970. 

The  strength  of  a  strip  of  the  plate  2\  inches  wide  is 

H  X  T\  X  55,000=  54,140. 

The  calculated  resistance  to  shearing  is  less  than  the 
resistance  to  tearing  or  compression.  The  apparent  effi- 
ciency of  the  joint  is 

31,063 

100  x  TTTT^  =  57-4  per  cent. 
54,140 

If  it  De  assumed  that  the  resistance  to  tearing  of  the 
section  between  rivets  will  have  an  excess  of  ten  per  cent 
over  the  resistance  of  a  piece  in  a  testing-machine,  then  the 
resistance  to  tearing  between  rivets  will  appear  to  be  34,740 
This  figure  is  not  far  from  the  resistance  to  shearing,  though 
still  inferior.      If  it  be  further  assumed  that  the  whole  plate 


STREXCTII    OF    BOILERS. 


outside  of  the  joint  will  show  a  tearing  strength  of  only 
55,000  pounds  per  square  inch,  the  efficiency  of  the  joint  will 
appear  to  be  more  than  five  per  cent  greater  than  that  given 
above.  It  is  probably  wise  to  ignore  the  excess  of  strength 
due  to  the  fact  that  the  plate  between  the  rivets  will  not 
draw  down  for  reasons  that  have  already  been  stated  at  length. 
Double-riveted  Lap-joint. — The  rivets  in  this  joint  may 
be  staggered  as  shown  by  Fig.  91,  or  chain-riveting  may  be 


Fig.  91. 

used  as  in  Fig.  92.      If  the  rivets  are  staggered  and  the  two 
rows  are  too  near  together,  it  is  possible  that  the  plate  may 


Fig.  92. 


tear  down  from  a  rivet  in  one  row  to  the  nearest  rivet  in  the 
next  row,  and  thus  have,  after  tearing,  a  jagged  edge.  With 
the  usual  proportions  such  a  failure  will  not  occur,  but  the 
plate  will  tear  between  rivets  in  the  same  row,  if  it  fails  by 


208  STEAM-BOILERS. 

tearing.     The  calculation  for  efficiency  will  consequently  be 
the  same  for  both  methods  of  riveting. 

Let  the  dimensions  be 

/  =  7/16,     d-  13/16,     p  =  l\. 

The  joint  may  fail  in  one  of  three  ways: 

1st.  Shearing  two  rivets.  The  assumed  strip  having  a 
width  equal  to  the  pitch  will  be  held  by  two  rivets;  this  is 
apparent  at  once  for  chain-riveting.  For  staggered  rivets 
such  a  strip  will  contain  one  whole  rivet  and  half  of  two 
others,  so  that  the  same  rule  holds.  The  resistance  of  two 
rivets  to  shearing  will  be 

2-^—ft  =  46,660. 
4 

2d.    Tearing  between  two  rivets.     The  resistance  is 

(P  -  d)tft  =  40,600 
3d.   Crushing  in  front  of  rivets.     Just  as  for  shearing,  we 
have  here  the  resistance  at  two  rivets  equal  to 

2dtf  =  67,540. 

The  strength  of  the  plate  for  a  width  of  the  pitch  is 

ptf  =  60, 160. 

The  plate  will  apparently  fail  by  tearing,  and  the  effi- 
ciency of  the  joint  will  be 

40,600       ^ 

100  X  5 7-  =  67.5  per  cent. 

60,160 

The  increase  of  efficiency  of  the  double-riveted  lap-joint 
over  the  single-riveted  joint  is  clearly  due  to  reducing  the 
diameter  of  the  rivet  and  increasing  the  pitch.  A  further 
increase  of  efficiency  could  be  obtained  by  using  three  rows  of 
rivets ;  this,  however,  is  practicable  only  for  thick  plates,  as 
we  are  liable  to  get  too  wide  a  pitch  for  sound  calking 

Single-riveted  Lap-joint,  Inside  Cover-plate — In  this 
joint  the  plates  are  lapped  and  joined  by  a  single  row  of  rivets: 


STRENGTH  OF  BOILERS. 


209 


and  a  plate  is  worked  inside  and  riveted  through  the  shell 
with  a  single  row  of  rivets,  which  are  spaced  twice  as  far  apart 
as  the  rivets  in  the  lap.  In  making  up  the  joint  all  three  rows 
of  rivets  may  be  driven  at  the  same  time.  The  lapped  joint 
only  is  calked  ;  the  pitch  of  rivets  through  the  lap  must  con- 
sequently be  small  enough  to  give  sound  calking.  The  outer 
rows  of  rivets  are  not  controlled  by  this  rule. 

We  will  here  consider  a  strip  having  the  width  a,  Fig.  93, 
equal  to  twice  the  pitch  of  the  rivets  in  the  lap.  Such  a  strip 
will  be  held  by  two  rivets  in  the  lap  and  by  one  rivet  in  an 
outer  row. 

Assume  the  following  dimensions: 

Thickness  of  shell  and  of  cover-plate,  t  =  5/16. 

Diameter  of  rivets  (iron),  d  =  3/4. 

Pitch  of  rivets  in  lap,  p  =  if. 

Pitch  of  outer  rows  of  rivets,  P=  3^. 

Shearing  resistance  of  iron  rivets  per  square  inch  or  fs  =s 
38,000  lbs. 

The  joint  may  fail  in  one  of  five  ways: 


/             — _ 

JO     0     0    O 

OQC 

)od)op 

0   c 

i 

/ 

Fig.  93- 
1st.    Tearing  between  outer  row  of  rivets.     The  resistance  i 

(P-d)tft=  47,270. 


2 1  o  STEA  M-BOILERS. 

2d.  Tearing  between  inner  row  of  rivets,  and  shear  big 
outer  row  of  rivets.     The  resistance  is 

(/>-  2d)tft+?ff,  =  51,150. 
4 

Since  the  rivets  are  iron,  f  =  38,000. 

3d.  SJiearing  three  rivets.     The  resistance  is 

~ f~  50,350. 

4 

4th.    Crushing  in  front  of  three  rivets.     The  resistance  is 

$tdfc  =  66,800. 

5  th.  Tearing  at  inner  row  of  rivets  and  crushing  in  front 
of  one  rivet  in  outer  rozv.     The  resistance  is 

{P  -  2d)tft  +  tdf  =  56,641. 

The  strength  of  a  strip  of  plate  3!  inches  wide  is 

///,  =  60, 160. 

The  least  resistance  is  offered  by  the  first  method,  giving 
for  the  efficiency 

47,270 
100  X  60,160  =  ;8,6  per  Cent- 

If  the  inside  cover-plate  is  thinner  than  the  shell,  addi- 
tional complication  will  be  introduced  into  the  calculations 
for  resistance. 

Double-riveted  Lap-joint  with  Inside  Cover-plate. — 
The  arrangement  of  this  joint  is  shown  by  Fig.  94.  Assume 
the  dimensions: 

Thickness  of  shell  and  of  cover-plate,  /  =  7/16. 

Diameter  of  rivets  (steel),  d  =  3/4. 

Pitch  of  rivets  in  lap,  2{l. 

Pitch  of  outer  rows  of  rivets,  P  =  4. 


STRENGTH  OF  BOILERS. 
The  methods  of  failure  are: 
1st.    Tearing  at  outer  row  of  rivets. 

Resistance  (/'  -  d)tft  =  78,210. 
2d.  Shearing  four  rivets. 

47Td* 

Resistance  — — fs  =  79,560. 
4 


21 1 


Fig.  94. 

3d.  Tearing  at  inner  row  and  shearing  outer  row  of  rivets. 
A  strip  having  the  width  of  the  pitch  of  the  outer  row  of 
rivets  will  be  weakened  at  the  rivets  in  the  lap  to  the  extent 
of  one  rivet-hole  and  half  another  rivet-hole.  The  resist- 
ance is 

TTd" 

(P-  l\d)tft  +  — /.  =  89,080. 

4th.    Crushing  in  front  of  four  rivets. 
Resistance  \tdfc  =  124,640. 

5th.  Tearing  at  inner  row  of  rivets  and  crushing  in  front 
of  one  rivet. 

Resistance  (/>—  i\d)tf  4-  tdf  -  100,350. 


2 1 2  STEA  M-  BOILERS. 

Strength  of  strip  4  inches  wide, 
Ptft  =96,250. 

^rr-      ■  78,210 

Efficiency  =  100  X  —? =  81.3  per  cent. 

Double-riveted  Butt-joint. — The  joint  shown  by  Fig. 
95  has  a  cover-plate  inside  and  another,  narrower,  outside. 
There  are  two  rows  of  rivets  on  each  side  of  the  joint.  The 
inner  rows  are  nearer  together  and  pass  through  both  cover- 
plates. 


Fig.  95. 

The  outer  row  of  rivets  are  wider  apart  and  pass  through 
the  inner  cover-plate  only. 

The  dimensions  assumed  are: 

Thickness  of  the  plate  and  of  both  cover-plates,  t  =  7/16. 

Diameter  of  rivets  (iron),  15/16  inch. 

Pitch  of  inner  row  of  rivets,  2f. 

Pitch  of  outer  row  of  rivets,  5^. 

There  are  five  ways  in  which  the  joint  may  fail: 
1st.    Tearing  at  outer  row  of  rivets.     The  resistance  is 

{P-d)tft=  103,770. 


STRENGTH  OF  BOILERS.  215 

2d.  Shearing  two  rivets  in  double  shear  and  one  in  single 
shear.  If  the  plate  pulls  out  from  between  the  cover-plates 
shearing  off  the  rivets,  then  the  rivets  in  the  inner  row  must 
be  sheared  through  on  both  sides  of  the  plate,  or  they  are  in 
double  shear.  The  outer  row  of  rivets  are  sheared  at  only  one 
place.  There  are,  consequently,  five  sections  of  rivets  to  be 
sheared  for  a  strip  as  wide  as  the  larger  pitch.  The  r< 
ance  is 

——/,=  131,100. 

4 

3d.  Tearing  at  inner  row  of  rivets  and  shearing  one  of  the 
outer  row  of  rivets.      The  resistance  is 

nd" 
(P-2d)tf  +  — /,  =  107,43c. 
4 

4th.    Crushing  in  front  of  three  rivets.      The  resistance  is 

$tdfc  =  116,880. 

5  th.  Crushing  in  front  of  two  rivets  and  shearing  one 
rivet.      The  resistance  is 

2tdf  +  — -ft  =  104, 140. 
4 

The  strength  of  a  strip  5^  inches  wide  is 

5iX  TV  Xf=  126,560. 

The  efficiency  is 

103,770 
100 — 7 — zr-  =  82  per  cent. 
126,560  L 

Triple-riveted  Butt-joint. — The  joint  shown  by  Fig.  96 
has  three  rows  of  rivets  on  each  side.  Two  rows  pass  through 
both  cover-plates,  and  the  third  or  outer  row  passes  through 
the  inner  cover-plate  only. 


214  STEAM-BOILERS. 

The  dimensions  are: 

Thickness  of  shell,  /  —  7/16. 
Thickness  of  both  cover-plates,  tc  =  3/8. 
Diameter  of  rivets  (steel),  d  =  15/16. 
Pitch,  inner  rows,  /  =  3§. 
Pitch,  outer  row,  P  =  j\. 


Fig.  96. 

The  joint  may  fail  in  one  of  five  ways: 

1st.    Tearing  at  cuter  row  of  rivets.      The  resistance  is 

{P-d)tft=  151,890. 

2d.   Shearing  four  rivets  in  double  shear  and  one  in  single 
shear.     The  resistance  is 


gnd 


■f=  279,450. 


3d.   By  tearing  at  middle  rote  of  rivets  {where  the  pitch  is 
3f  inches)  and  shearing  one  rivet.      The  resistance  is 

ndl 

(p-  2d)tf  +  —/;  =  160,340. 
4 


STRENGTH  OF  BOILERS-  2T5 

4th.  By  crushing  in  front  of  four  rivets  and  shearing 
one  rivet.     The  resistance  is 

nd* 

4dtf  -f— /  =  186,830. 
4 

5th.  By  crushing  in  front  of  five  rivets.  Four  of  these 
rivets  pass  through  both  cover-plates  and  will  crush  at  the 
shell-plate.  The  fifth  rivet  passes  through  the  inner  cover- 
plate  only,  and  will  crush  at  that  plate,  since  the  cover-plates 
are  thinner  than  the  shell-plate.      The  resistance  is 

4dtf  -f-  dt,f  =  189, 170. 

The  strength  of  a  strip  of  plate  "j\  inches  wide  is 

Ptft=  174,3/0. 

The  efficiency  is 

151,890 

100  X  =  87  per  cent. 

I74o70 

Quadruple  Riveted  Butt-joints  with  two  cover-plates. 
Fig.  97  shows  such  a  joint. 

Thickness  of  shell,  /  =  i '2  inch. 

Thickness  of  both  cover-plates,  tc  =  y  '16  inch 

Diameter  of  rivets  (steel),  </  =  15/16  inch. 

Pitch  of  inner  row,  />  =  3f  inches. 

Pitch  of  second  row,  p=$\  inches. 

Pitch  of  third  row,  P  =  t]\  inches. 

Pitch  of  outer  row,  P  =  i$  inches. 
The  joint  may  fail  in  one  of  eight  ways: 
1st.  Tearing  at  the  outer  row  of  rivets.     The  resistance  is 

(P  -d)ift  =  386,700. 

2d.  Tearing  at  th"  third  row  and  shearing  one  rivet  in  the 
outer  row.     The  resistance  is 

—  /- 

(P  -  2d)tft  +  —f  =  400,410. 

4 


2l6 


STEAM-BOILERS. 


3d.  Tearing  at  the  second  row  of  rivets  and  shearing  three 
rivets.    The  resistance  is 

,       xd2r 
(P  -  4d)tft  +  3  — fs  -  402,560. 

4 


Fig.  97. 

4//?.  Double  shearing  eight  rivets  and  single  shearing  three. 
The  resistance  is 

xeP. 

19— /,=  590,200. 
4 


5$.  Crushing  in  front  of  eight  rivets  and  single  shearing  three. 

The  resistance  is 

rrd2r 
Utfc  +  3— /s  =  449>44°- 
4 


STRENGTH    OF    BOILERS.  21 7 

6th.  Crushing  in  front  of  eleven  rivets.     The  resistance  is 

1 1  dtfc  =  489,840. 

yth.  Tearing  at  the  third  row  of  rivets  and  crushing  in  front 
of  one  rivet  in  the  outer  row.     The  resistance  is 

(P  -  2d) tf  +  dtfc  =  413,880. 

8th.  Tearing  at  the  second  row  of  rivets  and  crushing  in  front 
of  three  rivets.     The  resistance  is 

(P  -  4d)tft  +  T,dtfc  =  442,960. 

The  strength  of  the  solid  plate  is 

Ptf  =  41 2,500. 

__       _  .  .    386,700 

The  efficiency  is  ■ =  93.7  per  cent. 

J       412,500     yj  '  l 

Designing  Riveted  Joints. — One  element  of  the  design 
of  a  riveted  joint  is  to  secure  as  high  an  efficiency  for  the 
joint  as  is  consistent  with  other  requirements,  such  as  a  proper 
pitch  for  calking. 

A  consideration  of  the  example  of  a  single-riveted  lap- 
joint  will  show  that  the  efficiency  can  be  improved  by  increas- 
ing the  diameter  of  the  rivet  and  by  increasing  the  pitch.  In 
the  first  place,  since  the  joint  will  fail  by  tearing  between  the 
rivets,  simply  increasing  the  pitch  with  the  same  size  of  rivet 
will  give  a  greater  efficiency.  If  the  pitch  is  increased  till 
the  rivet  fails,  the  failure  will  be  by  shearing.  Now  the 
resistance  to  crushing  is  represented  by 

dtfc, 

while  the  resistance  to  shearing  is  represented  by 

ltd"1 


2l8  STEAM-BOILERS. 

that  is,  the  resistance  to  crushing  increases  proportionally  as 
the  diameter,  while  the  resistance  to  shearing  increases  as  the 
square  of  the  diameter.  The  shearing  resistance  increases  the 
more  rapidly,  and  can  be  made  equal  to  the  crushing  resist- 
ance by  using  a  larger  rivet.  Of  course  this  will  demand  a 
further  increase  of  pitch. 

In  the  case  of  the  single-riveted  lap-joint  now  under  dis- 
cussion, the  proper  proportions  for  a  joint  that  shall  be  equally 
strong  against  shearing,  tearing,  and  crushing  can  be  calculated 
directly.  The  usual  way  is  to  determine  the  diameter  of  the 
rivets  by  making  them  equally  strong  against  shearing  and 
crushing.  Equating  the  expressions  for  crushing  and  shearing 
resistance,  we  have 

dtfc  =  —A.     or     d  -  7  -. 
4  ft* 

For  the  case  in  hand  with  steel  plates  7/16  of  an  inch  thick, 
and  steel  rivets,  the  diameter  will  be 

=  9^000  4Xij  = 

45,000        n 

Having  the  diameter  of  the  rivets,  we  may  now  calculate 

the    pitch  by  equating  the  shearing  and  tearing  resistances, 

which  gives 

Ttd2  ^       ,  _    ,  fs  Ttd 

—f,  =  (j-d)tft,      or    p=j—+d. 

For  the  case  in  hand  we  have 


45,000  7T  1. 17     , 

F      55,0004  X  tV 
The  efficiency  of  the  joint  is  the  ratio  of  the  resistance  to 


STRENGTH  OF  B<^>7LERS. 


2ig 


tearing  between  the  rivets  to  the  strength  of  a  strip  of  plate 
having  a  width  equal  to  the  pitch,  so  that  the  efficiency  is 

fkP~d)t  =p-d 

fspt  P        ' 

In  the  case  in  hand  the  efficiency  is 
i    1-2  -  i.i; 


IOO 


o--' 


63.4  per  cent. 


But  the  pitch  calculated  in  this  method  is  too  great  for 
proper  calking  with  a  plate  of  the  given  thickness. 

The  double-riveted  lap-joint  has  three  possible  ways  of 
failure,  which  lead  to  two  equations  for  finding  the  diameter 
and  pitch  of  rivets.  Equating  the  shearing  and  crushing 
resistance  for  two  rivets,  we  have 

Ttd7  f   At 

2  --fs  =  2dtfc ,     or     d  =  J-j  ^, 

which  will  give  the  same  size  rivet  for  a  plate  of  a  given 
thickness  as  would  be  found  for  a  single-riveted  joint.  Now 
this  method  has  been  found  to  lead  to  too  large  a  rivet  for  a 
single-riveted  joint,  where  a  strip  having  a  width  equal  to  the 
pitch  carries  one  rivet.  In  the  double-riveted  joint  such  a 
strip  carries  two  rivets,  and  consequently  it  is  the  more  cer- 
tain that  the  method  proposed  will  give  too  large  a  rivet,  and 
of  course  too  large  a  pitch  for  proper  calking.  The  advan- 
tage of  double  riveting  is  that  smaller  rivets  may  be  used  to 
provide  the  requisite  shearing  resistance,  and  the  plate  may 
be  less  cut  away  at  the  section  between  rivets. 

In  designing  a  double-riveted  lap-joint  it  is  customary  to 
assume  a  diameter  for  the  rivets  and  then  determine  the  pitch 
by  equating  the  shearing  resistance  of  two  rivets  to  the  tear- 
ing resistance  between  the  rivets.  If  the  resulting  pitch  is  too 
large  for  proper  calking,  the  diameter  of  the  rivets  must   be 


220  STEAM-BOILERS. 

reduced.  If,  on  the  contrary,  the  resulting  pitch  is  less  than 
may  be  allowed,  a  slightly  larger  diameter  and  pitch  may  be 
used. 

A  design  of  a  joint  like  the  single-riveted  lap-joint  with 
inside  cover-plate,  which  has  a  wide  and  a  narrow  pitch, 
involves  some  difficulty  and  complexity.  The  fundamental 
idea  of  such  a  joint  is  to  make  the  resistance  to  tearing  at  the 
inner  row  of  rivets  (when  the  pitch  is  small)  plus  the  shearing 
of  the  outer  row  of  rivets  greater  than  the  resistance  to  tear- 
ing at  the  outer  row  of  rivets  (when  the  pitch  is  larger).  To 
insure  this  condition  we  may  proceed  as  follows:  Equate  the 
resistance  to  tearing- at  the  outer  row  of  rivets  to  the  resist- 
ance to  tearing  at  the  inner  row  plus  the  resistance  to  shearing 
one  rivet  at  the  outer  row.      This  gives 


{P  -  d)tft  =  {P-  2d)tft  +  ~fs, 

4 
whence 


The  result  is  the  minimum  diameter  of  rivets  allowable. 
We  may  now  choose  a  slightly  larger  diameter  of  rivets,  and 
then  determine  the  pitch  in  three  different  ways,  namely,  by 
equating  the  resistance  to  tearing  at  the  outer  row  of  rivets, 
in  succession,  to  the  resistance  to  shearing  of  three  rivets, 
to  the  resistance  to  crushing  in  front  of  three  rivets,  and 
to  the  resistance  to  tearing  between  the  inner  rows  of  rivets 
and  compression  before  one  rivet.  The  smallest  pitch 
obtained  will  be  the  correct  one  to  use  with  the  given  diam- 
eter of  rivet.  Should  the  efficiency  of  the  joint  be  unsatis- 
factory, an  attempt  may  be  made  to  raise  the  efficiency  by 
increasing  the  diameter  of  the  rivets. 


STRENGTH  OF  BOILERS.  221 

In  the  preceding  pages  it  has  been  assumed  that  the  strength 
of  a  rivet  in  double  shear  is  twice  that  of  a  rivet  in  single  shear. 
Many  designers  use  a  lower  value  per  square  inch  in  double 
shear  than  in  single  shear.  There  is  but  little  evidence  to  show 
that  there  is  any  justification  for  this. 

The  effects  of  crushing  and  shearing  are  so  combined  that  it 
is  difficult  to  get  any  data  on  double  shear  that  is  reliable.  A 
careful  study  of  all  the  tests  made  at  the  Watertown  Arsenal, 
and  of  those  made  at  the  Massachusetts  Institute  of  Tech- 
nology, failed  to  give  any  evidence  that  would  warrant  using 
a  lower  value  per  square  inch  for  double  shear  than  for  single 
shear. 

Practical  Considerations. — In  proportioning  a  riveted 
joint,  the  following  considerations,  some  of  which  have  already 
been  mentioned,  must  receive  attention: 

The  pitch  of  rivets  near  a  calked  edge  must  not  be  too  great 
for  proper  calking. 

Rivets  must  not  be  too  near  together  for  convenience  in 
driving. 

Punched  holes  must  have  a  diameter  greater  than  the 
thickness  of  the  plate. 

A  riveted  seam  must  contain  a  whole  number  of  rivets. 
Again,  it  is  desirable  that  similar  seams,  as  for  example  the 
longitudinal  seams  for  the  several  rings  of  a  cylindrical  boiler, 
shall  have  the  same  pitch. 

It  is  evident  that  the  design  of  a  boiler-joint  cannot  be 
considered  apart  from  the  general  design  of  the  boiler. 

Flues. — The  tendency  of  internal  pressure  in  a  thin  hol- 
low cylinder  is  to  give  it  a  true  cylindrical  shape;  conse- 
quently, with  fair  workmanship,  the  formulae  for  thin  hollow 
cylinders  may  be  applied  to  the  calculation  of  boiler-shells 
subjected  to  internal  pressure.  But  the  tendency  of  external 
pressure  is  to  exaggerate  any  imperfection  of  shape,  and 
cylindrical  flues  fail  by  collapsing. 


222  STEAM-BOILERS. 

The  pressure  at  which  a  flue  will  collapse  can  be  found  by 
direct  experiment  only. 

The  earliest  and  for  a  long  time  the  only  tests  on  the 
collapsing  of  flues  were  those  made  by  Fairbairn,  and  pub- 
lished in  the  Transactions  of  the  Royal  Society,  in  1858.  All 
of  the  tubes  tested  were  0.043  °f  an  mch  thick;  they  varied 
in  diameter  from  4  inches  to  12  inches,  and  in  length  from  20 
inches  to  60  inches.  From  these  tests  he  deduced  the  em- 
pirical formula 


806,300  X  t2Z9 


in  which  /  is  the  length  of  the  tube  in  feet  and  d  and  /  are 
the  diameter  and  thickness  in  inches,  while/  is  the  collapsing 
pressure  in  pounds  per  square  inch.  Sometimes  the  exponent 
of  /  is  made  2  instead  of  2.19,  for  sake  of  simplicity.  As  /is 
commonly  a  proper  fraction,  the  use  of  a  smaller  exponent 
will  give  a  higher  calculated  collapsing  pressure. 

The  tubes  in  this  series  were  too  small,  and  more  especially 
too  thin,  to  serve  as  a  proper  basis  for  the  calculation  of  boiler- 
flues.  It  is  quoted  because  it  has  been  widely  used,  and  is 
now  used  by  some  engineers.  It  sometimes  gives  a  calculated 
pressure  higher  and  sometimes  lower  than  that  at  which  flues 
will  collapse,  and  its  use  is  liable  to  lead  to  disappointment  if 
not  to  disaster. 

The  following  table  gives  the  results  of  some  tests  on 
larger  boiler-flues,  taken  from  Hutton's  "  Steam-boiler  Con- 
struction." The  table  gives  the  dimensions  and  the  actual 
collapsing  pressure,  and  also  the  collapsing  pressure  by  Fair- 
bairn's  rule  and  by  a  rule  proposed  by  Hutton. 


STRENGTH  OF  BOILERS. 


*23 


EXPERIMENTS    ON    THE   COLLAPSING    PRESSURE    OF    BOILER. 

FLUES 


Where  or  by  Whom  Made. 


By  Fairbairn 

By  Fairbairn 

By  Fairbairn 

By  Fairbairn 

Engineering  Dept.,  U.  S.  N. 

At  Greenock 

By  Knight 

By  Knight 

By  Kntght 

By  J.  Howden  &  Co.,  Glas- 
gow  


Dimensions. 

Collapsing  Press\ 
Pounds  per  Squar 

s« 

.c 

X    K 

c  c 

J 

j=ac 

rt  — 

c 

V    1 

c  — 

J<  0 

nd  by 
erimen 

ulated 
bairn's 

c-r. 

Hi 

H  Si 

0  X 

Ufa 

2 

3 

4 

5 

e 

7.87 

276 

5 

no 

109 

33-5 

360 

11 

99 

81 

42 

420 

12 

97 

78 

42 

300 

12 

127 

108 

54 

36 

8 

128 

3" 

38 

86 

16 

450 

740 

36 

24 

8 

235 

700 

36 

24 

12 

468 

156S 

36 

48 

12 

390 

7^4 

43 

23 

17 

840 

2758 

£  3 


a  C 
=  £ 


uX 

7 


114 

"3 

JOO 

119 

120 

436 
218 
490 
350 

842 


On  the  whole  the  rule  proposed  by  Hutton  gives  the  most 
concordant  results;  in  most  cases  Hutton's  rule  gives  a  cal- 
culated collapsing  pressure  that  is  smaller  than  the  actual 
collapsing  pressure;  in  no  case  is  the  calculated  result  very 
largely  in  excess.  Fairbairn's  rule  in  some  cases  shows  a  very 
close  agreement  with  experiment,  but  in  others  it  shows  a 
dangerous  excess. 

Hutton's  rule  is 

Q2 


JVT 


in    which    /    is   the    length    in    inches,    d    is    the    diameter    in 


224  STEAM-BOILERS. 

inches,  and  /  is  the  thickness  in  thirty-seconds  of  an  inch. 
C  is  a  constant  which  Hutton  makes  600  for  iron  and  660  for 
steel. 

Mr.  Michael  Longridge,  as  a  result  of  an  investigation  of 
many  boiler  flues,  most  of  which  have  endured  service  for 
years,  but  some  of  which  failed,  gives  a  rule  in  the  same  form 
but  with  a  constant  540  instead  of  600. 

For  oval  tubes  and  flues  it  is  recommended  that  the  above 
rules  be  applied,  using  for  the  diameter  twice  the  maximum 
radius  of  curvature. 

Strengthened  Flues. — It  is  clear  from  inspection  of  the 
preceding  table  of  tests  on  boiler-flues  that  the  collapsing 
pressure  decreases  as  the  length  of  the  flue  increases.  Account 
is  taken  of  this  in  Hutton's  formula,  by  introducing  the 
square  root  of  the  length  into  the  denominator  of  the  expres- 
sion for  calculating  the  collapsing  pressure  of  a  flue.  Stating 
the  proposition  in  the  converse  manner,  the  reason  why  a 
short  flue  is  the  stronger  is  that  the  ends  of  the  flue  are 
kept  in  a  circular  form  by  the  plates  to  which  the  flue  is 
riveted. 

It  has  been  customary  to  strengthen  plain  flues  by  the  aid 
of  rings  placed  at  regular  intervals.  The  section  of  a  ring 
made  of  angle-iron  is  shown  by  Fig.  o8tf.  The  ring  is  riveted 
to  the  flue  at  intervals,  a  thimble  being  placed  over  each  rivet 
to  give  space  for  circulation  of  water  between  the  ring  and 
the  flue.  The  rings  were  sometimes  solid,  made  of  one  piece 
of  angle-iron  bent  up  and  welded.  Most  frequently  the  ring 
was  in  halves,  which  were  merely  belted  together  at  the  joint. 
Such  rings  could  be  easily  removed  when  the  flue  was  taken 
out  of  the  boiler. 

A  better  method  of  strengthening  a  flue  is  to  make  it  of 
short  pieces  so  joined  at  the  ends  as  to  make  stiffening  rings. 
Fig.  98  shows  three  ways  in  which  this  can  be  done.  At  b 
is  shown  the  Adamson  ring,  formed  by  flanging  the  edges  of 


STRENGTH  OF  BOILERS. 


225 


the  short  lengths  of  flue  outwardly,  and  riveting  through  a 
welded  iron  ring.  At  c  is  shown  a  welded  ring  of  T  iron,  to 
which  the  short  lengths  can  be  riveted  without  flanging.     This 


Fig.  98. 

method  provides  for  calking  both  inside  and  outside.  It 
does  not  require  the  flue  to  be  flanged;  but  flanging  by 
machinery  is  rapid,  and  does  not  give  trouble  when  good  iron 
or  steel  is  used.  Material  that  will  not  stand  flanging  should 
not  be  used  for  flues.  At  d  is  shown  the  bowling  hoop-ring, 
which  has  the  advantage  that  it  provides  for  longitudinal 
expansion  of  the  flue. 

Flues  for  Scotch  and  other  marine  boilers  with  furnace- 
flues,  are  stiffened  by  transverse  or  helical  corrugations,  which 
provide  at  the  same  time  for  longitudinal  expansion.  A 
number  of  methods  of  corrugating  furnace-flues  will  be 
illustrated  in  connection  with  tests  given  on  the  following 
pages. 

Tests  on  Furnace-flues. — The  strength  of  corrugated  and 
other  stiffened  flues  can  be  determined  only  by  tests  on  full- 
sized  specimens".  The  following  tests  are  taken  from  a  paper 
by  Mr.  B.  D.  Morison,  read  before  the  Northeast  Coast  In- 
stitution of  Engineers  and  Shipbuilders. 


226 


5  TEA  M-BOILERS. 


Furnaces  made  with  Adamson  Joints. 

Tests  made  at  the  Works  of  Hall,  Russell  &  Co.,  Aberdeen,  in 
1882,  and  of  J.  Howden  &  Co.  in  Glasgow,  in  1887. 


^ 

,    . 

V  0 

£^ 

E-c 

umber  of  Ring 

■s. 

1° 

a 

IE  - 
S3   eg 

£ 

O  T 

c"jH 
U  0  ^ 

Date 

of 
Test. 

Length 

of 

Furnace. 

ean  Thick 
Plate. 

xternal  Di 
in     Inche 
Plain  Part 

reatest     D 

Diameter 

Part. 

Is 

~  3 

c  - 

r  = 

"c  u 

ollapsing 
cient   redu 
Steel  of  z 
Tensile, 

2 

«=. 

W 

O 

u 

u 

U 

1st  ring 

6  ft.  5!  in.  total 

i" 

length. 

2d  ring 

1882 

Length  of 

rings  : 

lSJ".    19 ",  19", 

and  20" 

7  ft.  \  in.  total 

4 

15" 

32     ' 

3d  ring 

1  5'' 
3T     ' 

4th  ring 
1" 

43 

9/64 

3d  ring 
at  700 

ist  ring 
at  840, 
2d  ring 

64,213 

61,918 

1887 

length. 

Length  of  each 

ring,  23" 

4 

43-09 

at  760, 
3d  ring 
at  840, 
4th  ring 
at  835 

64,240 

61,945 

Note. — No  record  of  tensile  strength  of  steel  ;  28  tons  per  square  inch 
assumed.  The  collapsing  coefficients  are  calculated  on  external  diameter  of 
furnace  over  plane  part. 


STRENGTH  OF  BOILERS. 


227 


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S  TEA  M-B  OILERS. 


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reduced  to 
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56,900 

48.548 
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Ultimate 
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STRENGTH   OF  BO/LEKS. 


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STRENGTH  OF  BOILERS. 


231 


Purves's  Patent  Furnaces. 


Official  Tests   made   at   Sir  John   Brown  &  Co. 's  Works  at 
Sheffield  in  i88q. 


Dec.  23,  1890 


Corrugations  spaced  9"  apart.  Not  very  full  records  kept. 

Note. — The  collapsing  coefficients  are  calculated  on  diameters  of  furnaces 
over  flats. 


S  TEA  M-  BOILERS. 


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STRENGTH   OF  BOILERS.  233 

Discussion  of  Results  of  Tests  on  Flues. — The  stress 

in  a  thin  hollow  cylinder  subjected  to  external  fluid  pressure 
may  be  calculated  by  an  equation  having  the  same  form  as 
that  for  a  cylinder  subjected  to  internal  pressure;  the  equa- 
tion may  be  deduced  by  a  similar  method.  Thus  the  stress 
will  be 

t ' 

in  which/  is  the  pressure  per  square  inch,  r  is  the  radius  and 
/  is  the  thickness,  both  in  inches.  In  the  table  we  have  a 
column  giving  the  coefficient  of  collapse  calculated  by  the 
expression 

PD 
T' 

in  which  Pis  the  pressure,  D  is  the  diameter,  and  T  is  the 
thickness.  The  coefficient  appears  consequently  to  be  twice  the 
compressive  stress  in  the  flue  at  the  time  of  collapsing.  This 
coefficient  is  fairly  regular  for  each  style  of  furnace,  and  is 
somewhere  near  the  tensile  strength  of  the  metal  from  which 
the  flue  is  made;  in  some  cases  it  is  less  and  in  some  more 
than  the  tensile  strength.  Now  soft  steel  in  the  form  of  short 
cylinders  will  begin  to  flow  when  the  compressive  stress  in  a 
testing-machine  is  about  equal  to  the  strength  of  pieces  used 
for  tensile  tests.  In  other  words,  the  tensile  and  compressive 
strengths  are  about  equal.  The  furnaces  tested  appear, 
then,  to  have  collapsed  when  the  compressive  .stress  was  half 
the  ultimate  compressive  strength  of  the  metal.  Now  the 
limit  of  elasticity  for  both  tension  and  compression,  for  soft 
steel,  is  about  half  the  ultimate  strength,  so  that  the  collapse 
occurred  somewhere  about  the  elastic  limit.  We  should  not, 
however,  attribute  too  much  importance  to  this  considera- 
tion, but  it  will  be  better  to  follow  ordinary  practice  and 
consider  the  equations  used  for  calculating  the  safe  working 


234  STEAM-BOILERS. 

pressure  on  flues  to  be  empirical,  and  to  depend  directly  on 
experiment. 

Rules  for  Working  Pressure  on  Flues. — There  are  three 
sets  of  rules  for  working  pressure  on  flues,  which  we  shall 
consider;  namely,  those  of  the  British  Board  of  Trade,  those 
of  Lloyd' s  Marine  Insurance  Underwriters,  and  those  of  the 
United  States  Inspectors  of  Steam-vessels.  These  rules  are 
changed  from  time  to  time,  and  include  certain  directions  to 
inspectors  that  need  not  be  given  here;  if  a  boiler  is  built  for 
inspection  under  these  or  any  other  rules  the  only  safe  way  is 
to  obtain  the  current  edition  of  the  rules  and  see  that  the 
boiler  conforms  thereto,  and  also  that  the  boiler  is  properly 
proportioned  according  to  the  best  information  that  can  be 
obtained  by  the  designer. 

Rules  for  Plain  Flues. — Both  Lloyd's  and  the  United 
States  Inspectors  rules  use  for  plain  flues  an  equation  in  the 
form 

n    89,600  x  r 

y~         LD 

in  which  P  is  the  working  pressure  in  pounds  per  square  inch, 
L  is  the  length  in  feet,  and  T  and  D  are  the  thickness  and 
diameter  in  inches.  This  is  Fairbairn's  equation  with  2 
instead  of  2.19  for  the  exponent  of  T,  and  with  a  constant 


806,300 
89;  600  =  , 


so  that  the  working  pressure  is  made  one  ninth  of  the  calcu- 
lated collapsing  pressure  by  Fairbairn's  rule.  The  use  of  so 
large  a  factor  as  nine  shows  that  the  rule  is  not  considered 
adequate.  Flues  designed  under  this  rule  will  probably  be 
strong  enough.  * 

The  Board  of  Trade  rule    differs  only  in  replacing  the 


STRENGTH    OF  BOILERS.  235 

factor  89,600  by  the  approximate  figure  99,000.  The  rules, 
however,  require   that  the  pressure  shall  not  be  greater  than 

8800  X  T 
P~         D       ' 

which  provides  that  the  stress  shall  not  exceed  4400  pounds 
per  square  inch.  For  corrugated,  ribbed,  or  grooved  furnaces 
(such  as  the  several  furnaces  for  which  tests  are  given)  both 
the  Board  of  Trade  and  the  Inspectors'  rules  give  for  the 
working  pressure 

14,000  X   T 
~D         ' 

in  which  Pis  the  working  pressure  in  pounds  on  the  square 
inch,  and  T  and  D  are  the  thickness  and  diameter  in  inches. 
This  rule  makes  the  working  stress  7000  pounds  per  square 
inch. 

Lloyd's  rule  for  these  furnaces  is  given  by  the  equation 

r      C{T-2) 

D      ' 

in  which  T  is  the  thickness  in  sixteenths  of  an  inch,  D  is  the 
diameter  in  inches,  measured  over  the  corrugations  or  ribs  of 
corrugated  or  ribbed  furnaces,  and  over  the  plain  part  of 
Holmes'  furnaces.  C  is  an  arbitrary  constant  having  the  fol- 
lowing values: 

C  =  1000  for  steel  corrugated  furnaces  when  the  tensile 
strength  of  the  material  is  under  26  tons,  and  corrugations  are 
6  inches  apart  and  i£  inches  deep. 

C=  1259  for  steel  furnaces  corrugated  on  Fox's  or  Mori- 
son's  plans,  tensile  strength  to  be  between  26  and  30  tons. 

C  =  1160  for  ribbed  furnaces  with  ribs  9  inches  apart. 

C=  912  for  spirally-corrugated  furnaces. 

C  =  945  for  Holmes'  furnaces,  when  corrugations  are  not 
over  16  inches  apart  and  not  less  than  two  inches  high. 


2^6 


5  TEA  M-BOIL  ERS. 


In  this  rule  the  use  of  T  —  2  (in  sixteenths  of  an  inch) 
instead  of  T  is  practically  an  allowance  for  wasting  of  the 
plate  to  the  extent  of  one  eighth  of  an  inch.  The  working- 
stress  calculated  on  the  assumed  diameter  will  be  found  by 
multiplying  by  sixteen  and  dividing  by  two;  in  case  of  the 
first  constant  the  stress  is 

iooo  X  16 
=  8ooo 

2 

pounds  per  square  inch. 

Fire-tubes. — The  thickness  usually  given  to  fire-tubes  to 
insure  sound  welding  and  to  provide  for  expanding  into  the 
tube-sheets  is  in  excess  of  that  required  to  prevent  collapsing. 
There  appears,  however,  to  be  no  experiments  to  show  the 
actual  collapsing  pressure  for  such  tubes. 

The  joint  made  by  expanding  the  tubes  into  the  tube- 
sheets  of  locomotive  and  cylindrical  tubular  boilers  has  been 
found  both  by  experiment  and  practice  to  be  strong  enough 
to  secure  the  tube-sheet  without  additional  staying.  It  is, 
however,  the  custom  to  make  part  of  the  fire-tubes  of  marine 
drum-boilers  thick  enough  to  take  a  shallow  nut  outside  of 
the  tube-plate;  without  such  stay-tubes  there  is  liable  to  be 
leakage  at  the  ends  of  the  tubes. 

Girders — When  a  flat  surface  cannot  conveniently  be 
stayed  directly,  it  is  customary  to  stay  the  surface  to  girders 
properly  supported  at  the  ends  or  elsewhere.  The  crown-bars 
of  the  locomotive-boiler  shown  on  Plate  II,  and  the  girders 
over  the  combustion-chamber  of  the  marine  boiler  shown  by 
Fig.  ii,  page  17,  may  be  taken  as  examples.  Again,  the 
channel-irons  which  are  riveted  to  the  flat  heads  of  the 
cylindrical  boiler  shown  by  Plate  I  act  as  girders. 

The  load  which  a  girder  of  given  material  can  safely  carry 
depends  on  the  form  and  dimensions  of  the  girder,  and  on  the 
manner  of  supporting  and  loading  the  girder.  Some  girders, 
like  those  over  the  combustion-chamber  in  Fig.   n,  can  be 


STKEXGTH   OF  BO  I  LEA'S.  237 

calculated  by  the  simple  theory  of  beams;  others,  like  crown- 
bars  for  locomotives  and  the  channel-bars  on  Plate  I,  can  be 
properly  calculated  only  by  the  theory  of  continuous  girders. 

A  proper  understanding  of  the  theories  of  beams  and  of 
continuous  girders  can  be  obtained  from  standard  works  on 
applied  mechanics.  An  adequate  statement  of  even  the 
theory  of  beams  is  out  of  place  in  a  work  on  boilers;  an 
incomplete  statement  is  unadvisable,  since  it  is  liable  to  be 
misleading.  One  simple  example  will  be  worked  out  as  an 
illustration  of  the  use  of  the  beam  theory  in  boiler-design. 

As  an  example,  we  will  take  the  girders  over  the  combus- 
tion-chamber of  the  marine  boiler  shown  by  Fig.  n,  page  17. 
The  girders  are  spaced  7  inches  apart,  and  each  carries  three 
stays  spaced  6\  indies  apart.  The  load  on  each  stay-bolt  at 
160  pounds  steam-pressure  is 

7X6{X  160  =  7000  pounds, 

and  the  total  load  on  one  girder  is  21,000  pounds.  The  sup- 
porting force  at  each  end  of  the  girder  is  10,500  pounds.  The 
span  of  the  girder  is  22^  inches,  and  the  half-span  is  \\\ 
inches.  The  bending-moment  at  the  middle  of  the  girder 
due  to  the  supporting  force  acting  upward,  and  to  the  load 
on  one  bolt  acting  downward,  is 

10,500  x  n|—  7000  X  6|  =  74,375  =  M. 

Each  girder  is  made  of  two  plates  each  5/8  of  an  inch  thick, 
and  7  inches  deep.  The  moment  of  inertia  of  the  section  of 
the  girder  at  the  middle  is 

TV  X  2  X  f  X  73  =  /• 
The  distance  of  the  most  strained  fibre  is 
7^2  =  3£=  y. 


2  $8  STEAM-BOILERS. 

The  working  fibre-stress  is  consequently 

/=jfr  74  375X3* 

pounds  per  square  inch. 

Stayed  Flat  Plates.  —  The  method  of  calculating  the 
stresses  in  a  flat  plate  supported  at  regular  intervals  by  stays 
or  stay-bolts,  such  as  the  sides  of  a  locomotive  fire-box,  is 
treated  in  the  theory  of  elasticity,  under  the  heading  of 
"  indefinite  plates  which  are  firmly  held  at  a  system  of  points 
dividing  them  into  rectangular  panels."  A  complete  solution 
of  this  problem  is  possible  only  when  the  panels  are  squares, 
that  is,  when  the  rows  of  stays  are  equidistant  longitudinally 
and  transversely. 

If  the  steam-pressure  is  represented  by/,  the  thickness  of 
the  plate  by  /,  and  the  pitch  of  the  stays  by  a,  then  the 
direct  working  stress,  which  is  a  tension  at  certain  places  and 
a  compression  at  others,  is  given  by  the  formula 

2d1 

The  maximum  deflection  is  given  by  the  equation 

I   pa" 

in  which  E  is  the  modulus  of  elasticity  of  the  material. 

If  the  sheets  of  a  locomotive  fire-box,  or  other  stayed 
plates,  have  a  direct  tension  or  compression,  proper  allowance 
must  be  made  for  it. 

If  stays  or  stay-bolts  are  in  rows  that  are  not  equidistant 
each  way,  as  for  example  the  through-stays  in  the  steam- 
space  in  Fig.  11,  page  17,  then  the  Jargest  pitch  may  be  used 
in  the  above  equations.  The  actual  stress  will  in  such  case  be 
less  than  the  calculated  stress  by  an  unknown  amount.      If, 


STRENGTH  OF  BOILERS.  239 

further,  stays  are  arranged  irregularly,  the  greatest  distance 
in  any  direction  may  be  used  in  the  equations,  but  the  calcu- 
lated stress  may  then  be  very  different  from  the  actual  stress : 
it  is,  however,  always  the  larger. 

As  an  example,  we  may  calculate  the  stress  in  a  side  sheet 
of  the  locomotive  fire-box  shown  on  Plate  II.  Here  the 
rows  of  rivets  are  four  inches  apart  each  way,  the  plate  is 
5/16  of  an  inch  thick,  and  tne  steam-pressure  is  170  pounds. 
The  maximum  stress  is 

/=i(Ar,70  =  6,9°- 

Now  the  crown-bars  are  bedded  on  and  are  partly  sup- 
ported by  the  side  sheets  of  the  fire-box.  The  crown-sheet 
is  72  inches  long  and  45 f  inches  wide,  and  has  an  area  of 

72  X  45l  =  3285 

square  inches,  and  is  subjected  to  a  pressure  of 

3285  X  170  =  558,450 

pounds.  The  distribution  of  this  load  between  the  side 
sheets  and  the  sling-stays  can  be  determined  only  by  the  cal- 
culation of  the  crown-bars  as  continuous  girders,  and  may  be 
disturbed  by  the  expansion  of  the  fire-box  and  by  other 
causes.  If  it  be  assumed  that  the  side  sheets  carry  half  the 
load  on  the  crown-bars,  then  one  side  sheet  will  carry  one 
fourth  of  558,050,  or  139,512  pounds.  The  side  sheet  is  72 
inches  long  and  5/16  of  an  inch  thick,  so  that  the  stress  per 
square  inch  from  the  load  on  the  crown-bars  is 

139,512  -=-  72  X  tV  =  62°° 

pounds, — about  as  much  as  the  stress  calculated  above.    The 


2  43  i"  TEA  M-BOIL  ERS. 

total  compression  on  the  side  sheet  is  therefore  about  12,400 
pounds  per  square  inch. 

This  calculation,  which  appears  sufficiently  simple,  illus- 
trates the  danger  of  making  calculations  by  formulae  without 
knowing  how  they  are  derived  and  how  they  should  be 
applied.  The  formula  for  staying  given  above  is  often 
quoted  without  any  reference  to  tensile  or  compressive  stress 
on  tne  stayed  sheet,  from  other  causes;  the  use  of  such  a 
formula  by  one  who  is  unfamiliar  with  the  theory  of  elasticity 
may  lead  to  serious  error  in  design. 

Factor  of  Safety. — The  reciprocal  of  the  ratio  of  the 
working  pressure  of  a  boiler  to  the  pressure  at  which  the 
boiler  or  any  part  of  a  boiler  may  be  expected  to  fail  quickly, 
is  called  the  factor  of  safety  for  the  boiler  or  for  that  part  of 
the  boiler. 

It  is  commonly  recommended  by  writers  that  a  factor  of 
safety  of  six  shall  be  used  for  boilers;  probably  such  a  factor 
would  be  economical  for  a  boiler  that  is  expected  to  work 
continuously  for  many  years,  as  it  allows  a  margin  for  deteri- 
oration. If  the  stresses  coming  on  the  parts  of  a  boiler  can 
be  determined,  a  general  factor  of  five  will  give  sufficient 
security.  If  the  boiler  is  carefully  watched,  a  factor  of  four 
may  be  used;  many  boilers  are  worked  with  this  factor.  The 
use  of  an  excessively  large  factor  of  safety,  for  example  of  the 
factor  nine  for  flues  calculated  by  Fairbairn's  equation,  shows 
a  lack  of  confidence  in  the  method.  It  is  proper  to  make 
allowance  for  corrosion  of  parts  like  stays:  this  may  be  done 
either  by  using  a  larger  factor  of  safety,  or  by  a  direct  allow- 
ance; thus  all  stays,  whatever  their  diameters,  may  have  an 
eighth  of  an  inch  added  to  the  diameter  to  allow  for  corrosion. 
It  is  of  course  proper  in  any  structure  to  make  small  but  im- 
portant members,  such  as  stays  in  boilers,  large  enough  to 
place  them  beyond  any  suspicion  of  failure. 

Hydraulic  Tests  of  Boilers. — It  is  customary  to  subject 
new  boilers  to  a  water-piessure  considerably  in  excess  of  the 
working  pressure,  to  discover  any  leaks  at  riveted  joints,  at 


STRENGTH    OF  BOILERS.  24 1 

the  tube-sheets,  or  elsewhere;  should  there  be  any  gross 
defect  of  design  or  workmanship  it  will  be  developed  by  this 
hydraulic  test.  Old  boilers  after  repairs  are  subjected  to  a 
hydraulic  test  for  the  same  purpose,  but  the  pressure  is  not 
carried  so  high  as  for  new  boilers. 

The  pressure  applied  during  a  hydraulic  test  is  seldom 
more  than  once  and  a  half  the  working  pressure,  and  as  most 
boilers  have  an  actual  factor  of  safety  of  not  more  than  five, 
and  frequently  of  four,  it  is  apparent  that  the  recommenda- 
tion of  some  authors,  that  the  test  pressure  should  be  twice 
the  working  pressure,  cannot  ordinarily  be  followed  without 
danger  of  injuring  the  boiler.  With  a  factor  of  safety  of  six 
there  should  be  no  danger  of  injuring  the  boiler  by  applying 
a  hydraulic  pressure  equal  to  twice  the  working  pressure. 

It  should  be  borne  in  mind  that  some  of  the  worst  stresses 
that  come  on  the  different  parts  of  the  boilers  are  due  to 
unequal  expansion  and  contraction,  and  that  such  stresses  are 
not  set  up  during  a  hydraulic  test.  Finally,  the  fact  that  a 
boiler  has  successfully  withstood  a  hydraulic  test  is  not  a  con- 
clusive proof  that  it  is  safe;  too  many  unfortunate  explosions 
of  boilers,  more  frequently  old  boilers,  after  a  hydraulic  test, 
have  shown  this. 

The  safety  of  a  boiler  is  to  be  insured  by  careful  and  cor- 
rect design,  honest  and  thorough  workmanship,  and  intelli- 
gent care  in  service.  Forms  and  methods  of  design  and 
construction  that  do  not  admit  of  ready  calculation  should  be 
avoided;  in  no  case  should  the  ordinary  hydraulic  test  be 
relied  upon  to  guarantee  the  strength  of  parts  that  cannot  be 
calculated  with  a  fair  degree  of  certainty.  If  such  forms  are 
used  in  any  case,  they  ought  to  be  tested  separately  to  a 
pressure  of  two  or  three  times  the  working  pressure,  and  some 
examples  of  each  form  and  size  ought  to  be  tested  to  destruc- 
tion. 

The  boiler  undergoing  a  hydraulic  test  should  be  carefully 
inspected,  and  any  notable  change  of  shape  or  leakage  should 


242  STEAM-BOILERS. 

be  investigated  to  discover  the  cause.  Frequently  small  leaks 
that  are  developed  during  a  test  are  stopped  at  once  by- 
calking  or  otherwise,  but  it  is  preferable  to  mark  the  place 
of  the  leak  and  calk  after  the  pressure  is  removed.  This  of 
course  requires  another  test  to  find  out  if  the  calking  is  suc- 
cessful. 

The  pressure  is  usually  applied  by  filling  the  boiler  entirely 
full  of  water  and  then  pumping  in  enough  water,  by  hand  or 
by  power,  to  supply  the  leaks  and  develop  the  pressure 
required.  If  the  pumping  is  done  by  hand,  it  is  desirable  to 
carefully  remove  all  air  from  the  boiler  to  avoid  the  labor  of 
compressing  air  up  to  the  test  pressure.  If  the  pumping  is 
done  by  power,  the  saving  of  work  is  of  less  consequence,  and 
a  little  air  remaining  in  the  boiler  will  act  as  a  cushion,  and 
lessen  the  shocks  due  to  the  strokes  of  the  pump. 

New  boilers  are  tested  on  the  boiler-shop  floor;  old  boilers 
are  commonly  tested  in  their  settings,  and  in  such  case  the 
inspection  during  a  test  is  less  convenient  and  efficient. 

It  is  sometimes  recommended  that  hot  water  snail  be  used 
for  testing  a  boiler;  but  there  seems  to  be  no  advantage  in 
so  doing,  as  it  is  unequal  expansion,  and  not  merely  rise  of 
temperature,  that  sets  up  the  unknown  stresses  that  are  so 
destructive  to  the  boiler.  Of  course  the  use  of  hot  water 
makes  an  efficient  inspection  during  the  test  difficult  if  not 
impossible. 

When  there  is  no  other  way  of  applying  the  hydraulic  test 
to  a  boiler  in  its  setting,  the  boiler  may  be  quite  filled  with 
water,  and  then  a  light  fire  may  be  started  in  the  furnace. 
The  expansion  of  the  water  will  develop  the  required  pressure 
at  a  much  less  temperature  than  that  of  steam  at  the  same 
pressure,  and  with  less  danger  should  the  boiler  fail.  This 
method  cannot  be  recommended  for  general  use;  and  in  case 
it  is  followed  care  must  be  taken  not  to  exceed  the  desired 
pressure. 


STREXCTH  OF   BOILERS.  243 

Hydraulic  Test  to  Destruction. — In  1888  a  boiler-shell, 
made  to  represent  a  part  of  the  shell  of  a  gunboat  boiler,  was 
tested  by  hydraulic  pressure  at  the  Greenock  Foundry,"  with 
the  intention  of  bursting  it.  The  shell  was  1 1  feet  long  and 
7  feet  8T3T  inches  mean  diameter.  It  was  made  of  three  sec- 
tions of  19/32  plate,  triple-riveted,  with  butt-joints  and  double 
cover-plates  at  the  longitudinal  joints,  and  lapped  and  double 
riveted  at  the  ring  seams.  The  rivets  were  staggered  for  both 
longitudinal  and  ring  seams.  The  end-plates  were  20/32 
thick,  and  stayed  with  through-stays  and  washers,  spaced  14 
inches  on  centres.  The  stays  were  if  inches  in  diameter; 
the  screws  at  the  ends  of  the  stays  were  2\  inches  in  diameter. 
Finally,  it  may  be  said  that  the  shell  was  designed  to  fulfil 
the  Admiralty  specifications  for  a  working  pressure  of  145 
pounds  per  square  inch.  The  workmanship  was  of  the  same 
degree  of  excellence  usual  for  boiler-work  at  that  establish- 
ment. 

First  Test. — The  shell  was  first  subjected  to  the  working 
pressure  of  145  pounds,  and  showed  a  slight  alteration  of  form 
due  to  the  tendency  of  internal  pressure  to  give  it  a  true  cylin- 
drical form.  The  pressure  was  then  raised  to  the  Admiralty 
test  pressure  of  235  pounds,  and  then  to  300  pounds  without 
developing  leaks.  There  were  some  minor  changes  of  form 
due  to  the  increase  of  pressure.  The  pressure  was  then 
removed  and  the  shell  returned  to  its  original  dimensions. 

Pressure  was  then  raised  to  330  pounds,  when  there  was  a 
slight  leak  at  the  manhole  door.  At  450  pounds  pressure 
the  leak  at  the  manhole  door  exceeded  the  capacity  of  the 
pumps.  There  was  also  a  slight  leak  at  the  corners  of  two 
butts.  The  manhole  was  then  strengthened — no  other  repairs 
~were  made. 

Second  Test. — Pressure  was  raised  to  350  pounds  and 
developed  a  small  leak  at  the  manhole.      There  were  slight 

*  Trans.  Inst.  Naval  Arch.,  vol.  xxx.  p.  285. 


244  STEAM-BOILERS. 

leaks  at  the  butt-straps,  which  were  calked  at  the  end  of  the 
test.  The  manhole,  however,  leaked  so  that  the  test  was 
stopped. 

Third  Test. — After  additional  bolts  were  put  into  the 
manhole  cover  the  pressure  was  raised  to  350  pounds  with- 
out leakage.  At  360  pounds  the  manhole  began  to  leak,  and 
at  580  pounds  the  test  was  stopped  on  that  account.  The 
butt-straps  opened  visibly  at  the  calking  and  leaked  more 
than  before. 

Fourth  Test. — The  butt-joints  were  again  calked  and 
additional  pumps  were  employed.  The  shell  was  again  tight 
at  350  pounds  and  the  pressure  was  carried  to  620  pounds,  at 
which  there  was  a  good  deal  of  leakage  at  the  butt-straps. 
Only  one  or  two  rivets  showed  signs  of  leakage;  there 
appeared  to  be  no  difference  between  the  hand  and  machine 
riveting  in  this  respect.  At  the  pressure  of  620  pounds  the 
entire  capacity  of  the  pumps  was  required  to  supply  the 
leakage. 

The  distortion  of  the  shell  was  very  marked  at  the  higher 
pressures,  and  increased  with  the  pressure;  thus  the  ends 
bulged  an  inch  at  520  pounds,  about  \\  inches  at  580  pounds, 
and  nearly  two  inches  at  620  pounds.  The  sides  bulged  more 
irregularly,  but  to  the  extent  of  nearly  an  inch  at  620  pounds. 
The  stays  drew  down  uniformly  1/64  of  an  inch  at  520 
pounds,  2/64  at  580  pounds,  and  4/64  at  620  pounds.,  They 
increased  in  length  27V  inches  at  520  pounds,  3^  inches  at 
580  pounds,  and  3!  inches  at  620  pounds;  this  accounts  for 
the  bulging  of  the  end-plates. 

The  mean  tensional  strength  of  the  plates  from  which  tlie 
shell  and  butt-straps  were  made  may  be  taken  at  61 ;  500 
pounds.  At  620  pounds  the  tension  on  the  plates  between 
the  rivet-holes  was  57,504  pounds,  or  93^  per  cent  of  the 
strength  of  the  solid  plate,  and  there  was  no  serious  disturb- 
ance of  the  structure.  The  ring  seams  increased  in  diameter 
about  %  of  an  inch,  and  the  shell  bulged  out  between  them. 


STRENGTH  OF  BOILERS.  245 

The  various  portions  of  the  boiler  acted  in  harmony  and 
showed  no  special  weakness  at  any  point.  The  butt-joints 
had  the  rivets  spaced  5f  inches  on  centres  to  give  a  percen- 
tage of  83.7  per  cent  of  the  plate,  and  this  may  have  caused 
the  leakage  found  there.  The  riveting  appeared  to  be 
reliable  at  the  extreme  pressure  reached.  This  test  seems  to 
show  that  a  boiler  will  give  signs  of  weakness  long  before  it 
will  fail.  Such  signs  of  weakness  should  be  carefully  investi- 
gated:  if  there  is  any  local  weakness  or  deterioration,  repairs 
or  alterations  may  be  made;  if  there  are  evidences  of  general 
deterioration,  the  working  pressure  must  be  reduced,  or 
better,  the  boiler  may  be  replaced  by  a  new  one. 

Boiler-explosions. — The  great  destruction  of  life  and 
property  that  is  liable  to  be  caused  by  a  violent  boiler-explo- 
sion makes  it  imperative  that  the  causes  should  be  carefully 
investigated,  to  the  end  that  explosions  may  be  prevented. 

With  this  in  view  the  boiler  and  its  parts,  and  any  wreck 
or  evidence  of  destruction  caused  by  the  explosion  should  be 
left  undisturbed  until  the  scene  of  the  explosion  can  be 
examined  by  a  competent  engineer.  Of  course  if  any  persons 
are  injured  by  the  explosion  they  must  be  rescued  and  cared 
for  immediately,  and  also  any  building  or  structure  that  is  so 
injured  as  to  threaten  life  or  safety  must  be  attended  to  at 
once;  but  it  should  be  borne  in  mind  that  the  examination  by 
the  engineer  for  the  purpose  of  determining  the  cause  of  the 
explosion  is  also  in  the  interest  of  humanity,  since  its  aim  is 
to  avoid  future  explosions.  All  idle  or  simply  curious  per- 
sons should  be  excluded  from  the  scene  of  the  explosion,  more 
especially  as  such  persons  are  apt  to  disturb  or  even  carry 
away  things  that  may  be  of  importance  in  the  study  of  the 
cause  and  history  of  the  explosion.  If  the  explosion  is 
accompanied  by  loss  of  life  or  injury  to  person  or  property, 
it  will  be  followed  by  a  leg^al  investigation  in  which  the  testi- 
mony of  the  engineer  or  engineers  who  have  examined  the 
scene  of  the  explosion  will  be  of  prime  importance,  as  it  will 


2  46  S  TEA  M-B  O IL  ERS. 

have  a  large  influence  in  locating  responsibility  for  the 
disaster. 

While  various  causes  may  lead  to  boiler-explosion,  it  is 
unfortunately  true  that  by  far  the  greater  part  of  violent 
explosions  are  due  to  the  fact  that  the  boiler  is  too  weak  to 
endure  service  at  the  regular  working  pressure.  A  new  boiler 
may  be  weak  through  defective  design  or  workmanship; 
there  can  be  no  excuse  for  the  explosion  of  a  new  boiler  from 
weakness,  and  such  explosions  in  good  practice  are  rare.  An 
old  boiler  is  liable  to  become  weak  through  local  or  general 
corrosion  or  other  deterioration;  this  amounts  to  saying  that 
a  boiler  will  eventually  wear  out. 

The  length  of  time  that  a  boiler  will  endure  service 
depends  (1)  on  the  design,  (2)  on  the  thickness  of  plates  and 
the  quality  of  the  metal,  (3)  on  the  workmanship,  (4)  on  the 
care  given  it,  and  (5)  on  the  quality  of  the  feed-water. 
Definite  figures  cannot  be  given  for  the  life  of  a  boiler,  since 
it  depends  on  so  many  things.  The  following  table  gives  the 
number  of  years  several  kinds  of  boilers  can  endure  regular 
service  if  they  are  properly  built  and  cared  for: 

Lancashire,  low-pressure 1 5  to  20  years. 

Locomotive  type,  stationary 12  to  1  5 

Locomotive-boilers 8  to  1 2 

Vertical  boilers 10  to  15 

Vertical  boiler  with  submerged  tubes....  14  to  18 

Horizontal  cylindrical  tuoular ....  1 5  to  20 

Scotch  marine  boiler 12  to  1 5 

Water-tube  boiler 12  to  16 

Pipe  or  coil  boiler 5  to    8 

By  water-tube  boiler  is  here  meant  a  boiler  with  a  shell 
or  drum  containing  a  considerable  body  of  water.  By  pipe 
or  coil  boiler  is  meant  a  boiler  made  up  of  pipe  and  pipe- 
fittings,  with  a  separator. 


STRENGTH   OF  BOILERS. 


^47 


Horizontal  boilers  will  require  one,  and  vertical  boilers  two 
extra  sets  of  tubes,  before  the  shell  is  condemned.  A  loco- 
motive-boiler will  require  two  extra  sets  of  tubes,  and  the 
entire  fire-box  will  be  renewed  once  in  the  life  of  the  boiler. 

If  boilers  are  subjected  to  careless  or  ignorant  abuse,  they 
may  be  used  up  in  a  fraction  of  their  proper  time  of  service, 
especially  if  cheaply  built.  This  will  account  for  the  numer- 
ous explosions  of  sawmill  boilers  and  agricultural  boilers. 

It  has  been  pointed  out  that  leakage  is  frequently  a  sign 
of  weakness;  a  perversion  of  this  idea  leads  to  the  assumption 
that  a  boiler  is  safe  as  long  as  it  can  be  kept  from  leaking. 
Too  many  boiler-explosions  have  this  history :  The  boiler, 
after  long  and  satisfactory  service,  began  to  leak;  a  cheap 
man  was  employed  to  repair  the  boiler,  the  repairs  consisting 
mainly  of  excessive  calking  to  stop  the  leaks;  soon  after  the 
repairs,  perhaps  the  first  time  the  boiler  was  fired  up,  it 
exploded  violently.  A  fit  conclusion  of  the  history  is  to 
ascribe  the  explosion  to  some  obscure  cause  or  to  carelessness 
of  the  attendant,  if  he  was  killed  by  the  explosion. 

Serious  injury  may  be  caused  by  overheating  any  part  of 
the  heating-surface,  due  to  low  water,  to  defective  circulation, 
or  to  deposits  of  non-conducting  substance  on  the  plates  or 
tubes.  The  overheated  member,  or  plates,  of  the  boiler  may 
burst  or  collapse,  and  such  failure  may  lead  to  an  explosion 
of  the  boiler,  but  frequently  the  escape  of  steam  and  water 
will  check  the  fire  and  relieve  the  pressure  on  the  boiler. 
Local  failures  are  dangerous  to  the  boiler  attendants,  especially 
in  a  confined  fire-room,  as  on  shipboard.  Unless  there  is 
direct  evidence  of  overheating,  either  from  known  circum- 
stances before  the  explosion  or  from  signs  on  the  boiler  after 
explosion,  the  cause  of  the  failure  should  be  sought  elsewhere. 

If  a  boiler  shows  signs  of  low  water  or  of  overheating  the 
■fire  should  be  checked  by  any  effectual  means.  The  most 
ready  way  of  checking  the  fire  is  to  close  the  ash-pit  doors  and 
throw  ashes  onto  the  fire.      If  there  are  no  ashes  at  hand,  then 


248  STEAM-BOILERS. 

fresh  fuel  may  be  used  instead,  since  its  first  effect  is  to  deaden 
the  fire.  There  will  be  time  for  caring  for,  or  drawing  the  fire 
before  the  fresh  fuel  is  fairly  in  combustion.  An  attempt  to 
draw  the  fire  without  first  deadening  it  is  liable  to  give  a  fierce 
combustion  for  a  short  time;  moreover,  more  time  is  required 
to  draw  the  fire.  If  the  furnace  has  a  dumping-grate,  the  fire 
may  be  immediately  thrown  into  the  ash-pit  without  waiting 
to  deaden  it.  The  damper  should  be  left  open  so  that  if  a 
rupture  occurs  the  steam  may  escape  up  ^he  chimney.  Mean- 
while the  steam  made  by  the  boiler  should  be  disposed  of  by 
allowing  the  engine  to  run  or  by  any  other  means,  for  exam- 
ple by  opening  the  safety-valve,  provided  that  it  is  merely  a 
case  of  overheating,  not  accompanied  by  excessive  pressure. 
It  will  probably  be  well  to  start  the  feed-pumps  or  to  increase 
the  supply  of  feed-water.  Should  the  introduction  of  feed- 
water  be  badly  arranged  so  that  a  large  volume  of  cold  water 
will  be  thrown  onto  a  heated  plate,  it  is  possible  that  starting 
the  feed-pump  may  cause  a  contraction  which  will  start  a 
rupture. 

It  has  been  found  by  experiment  that  boiler-flues  that 
have  been  purposely  allowed  to  become  bare  and  overheated 
have  been  saved  by  suddenly  directing  a  stream  of  cold  feed- 
water  upon  them,  though  such  treatment  may  make  them 
leak  at  the  joints.  The  heat  stored  in  such  hot  plates  is 
insignificant  as  compared  with  the  heat  in  the  water  and  steam 
in  the  boiler. 

Excessive  pressure,  especially  if  it  is  enough  to  give  good 
reason  to  fear  an  explosion,  is  more  difficult  to  deal  with;  the 
chances  of  success  are  less  and  the  risks  are  greater  than  when 
the  water  is  low,  but  the  pressure  is  not  excessive.  If  possi- 
ble the  fire  should  be  checked  and  the  pressure  relieved.  The 
first  may  be  done  by  throwing  on  ashes  or  cold  fuel,  and  the 
second  by  running  the  engine  at  full  load.  It  is  at  least 
doubtful  whether  starting  the  feed-pump  will  reduce  the 
pressure  fast  enough  to  do  much  good,  and  on  the  other  hand 


STRENGTH  OF  BOILERS.  249 

there  may  be  cases  where  such  action  would  start  an  explo- 
sion. It  is  not  best  to  open  the  safety-valve,  since  the  sudden 
opening  of  a  large  safety-valve  gives  a  shock  which  may 
determine  the  explosion.  Some  explosions  have  been  re- 
ported that  occurred  immediately  after  the  safety-valve 
opened. 

A  large  amount  of  energy  is  stored  in  the  steam  and  water 
in  a  boiler  in  the  form  of  heat.  An  idea  of  the  amount  of 
energy  in  any  given  case  may  be  obtained  by  a  simple  calcu- 
lation. Thus  the  cylindrical  boiler  shown  on  Plate  I,  at  150 
pounds  pressure  by  the  gauge,  will  contain  6600  pounds  of 
water  and  22  pounds  of  steam. 

The  total  weight  of  water  and  steam  is  6622.     The  fractional 

22 
weight  which  in  steam  is  — — =.00^2.     Should  the  boiler  ex- 

6622  °° 

plode  the  mixture  of  water  and  steam  would  expand  adiabati- 
cally  to  atmospheric  pressure.  A  portion  of  the  water  would 
have  vaporized.  The  percentage  of  the  entire  weight  which  is 
steam  after  the  explosion  has  taken  place  may  be  found  by  equat- 
ing the  entropy  at  the  two  points. 

Calling  xi  the  fractional  weight  which  is  steam  at  the  start 
and  x2  the  fractional  weight  at  2120;  )\  and  r2  the  heats  of  vapori- 
zation at  boiler  pressure  and  at  2120  respectively,  Tx  and  T2 
the  absolute  temperatures,  and  #1   and  02  the  entropies  of  the 

liquid  we  have  that   -7^  +  #1  =  ~L  +  d2.     If  we  call  the  boiler 
j  1  1  2 

pressure  165  pounds  absolute 

.00332X856.9  *2Xo6o-7 

365.9+459-5  _h'5  35     459-5+2i2+-jI^' 

#2  = -15,  or  about  15  per  cent  is  steam. 

The  work  done  comes  from  loss  of  intrinsic  energy  and  is  in 
this  case  equal  to 

6622  X  778(9!  +*i<oi  -q2-x2p2), 


25O  STEAM-BOILERS. 

where  </i  and  q2  are  the  heats  of  the  liquid  at  the  two  pressures 
and  p\  and  p2  are  the  internal  latent  heats.  Substituting  values 
for  these,  the  expression  reduces  to  6622  XjjS(^^y. 7  +.00332  X 
772.9- 180.3  —  .15 X896.9)  =  130,000,000  foot-pounds. 

If  the  entire  explosion  took  place  in  two  seconds,  work  was 
developed  at  the  rate  of  120,300  horse-power. 

If  a  calculation  is  made  for  this  same  boiler,  assuming  that  the 
boiler  was  "dry,"  or  just  filled  with  steam,  the  energy  developed 
would  be  between  5  and  6  million  foot-pounds  instead  of  130 
million. 

A  person  can  sometimes  judge  as  to  whether  the  boiler  was 
dry  or  not  at  the  time  of  the  explosion  bv  the  amount  of  destruc- 
tion caused  by  the  explosion. 

The  more  water  a  boiler  contains  the  greater  the  damage  done 
by  an  explosion. 

An  explosion  of  a  boiler  carrying  low  pressure  for  heating  will, 
if  there  is  a  considerable  amount  of  water  in  the  boiler,  develop  a 
number  of  millions  of  foot-pounds  of  energy. 

Lap-seam  Boilers. — It  has  already  been  mentioned  that 
pressure  on  the  inside  of  a  cylinder  tends  to  bend  out  any  flat 
places  and  to  make  the  shell  a  true  circle,  while  pressure  on  the 
outside  of  a  cylinder  tends  to  make  the  cylinder  collapse.  Any 
flat  places  in  such  a  cylinder  will  make  the  cylinder  collapse  at  a 
much  less  pressure.  This  has  been  shown  by  experiments  on 
upright  boilers.  The  fire-box  always  begins  to  collapse  at  the 
seams  where  one  part  of  the  circle  laps  over  the  other  part  because 
at  this  spot  there  is  a  flattened  area.  If  in  the  staying  of  the 
water-leg  of  a  vertical  boiler  an  extra  line  of  screwed  stay-rivets 
be  put  through  this  joint  the  collapsing  pressure  will  be  raised 
from  15  to  20  per  cent. 

The  longitudinal  joint  on  a  horizontal  multitubular  boiler 
comes  from  2  to  6  inches  above  the  top  of  the  brackets  support- 
ing the  boiler.  There  is  considerable  stress  thrown  into  the  joint 
by  the  load  on  the  brackets.  The  tendency  of  the  pressure  inside 
of  the  boiler  and  the  tension  in  the  shell  is  to  pull  the  flattened 


STEEXGTH  OF  BOILERS. 


25I 


area  at  the  joint  into  a  true  circle.  The  bending  takes  place  at 
the  rivet  holes.  The  force  tending  to  pull  the  joint  into  a  circle 
varies  every  time  the  boiler  pressure  changes.  These  repeated 
bendings  may  after  a  long  period  start  a  crack  which  gradually 
gets  deeper  and  finally  determnies  the  life  of  the  boiler. 

Sometimes  an  internal  inspection  of  the  boiler  may  show  such 
cracks,  but  more  often  the  crack  starts  between  the  two  plates 
where  one  laps  over  the  other.  A  crack  in  this  place  could  not 
be  found  either  by  an  internal  inspection  or  by  an  external  inspec- 
tion. A  cold-water  test  might  show  this  defect  if  the  water 
pressure  was  made  great  enough. 

A  number  of  boiler  explosions  have  resulted  from  cracks  of 
this  sort. 

A  lap-seam  boiler  may  wear  out  before  this  repeated  bending 
action  at  the  joint  starts  a  crack.  If  the  plate  used  was  ductile 
and  the  workmanship  was  good  such  probably  would  be  the  case. 


CHAPTER   IX. 
BOILER   ACCESSORIES. 

In  this  chapter  will  be  described  various  fittings,  attach- 
ments, and  accessories  for  steam-boilers. 

Valves  are  used  to  control  and  regulate  the  flow  of  fluids 
in  pipes.  They  are  variously  named  after  their  forms  or  uses, 
such  as  globe  valves,  angle-valves,  straightway  valves,  and 
check-valves. 


Fig.  99. 

Globe  Valves  are  named  from  the  globular  form  of  their 

cases.     The  case  is  separated  into  two  parts  by  a  diaphragm 

with  a  passage  through  its  horizontal  part,  as  shown  in  Fig. 

99.     The  fluid  enters  at  the  right,  passes  under  the  valve,  and 

252 


BOILER   ACCESSORIES. 


-?.- 


out  at  the  left.  The  valve  is  shut  by  screwing  down  the 
handle  on  the  valve-spindle.  A  stuffing-box  around  the 
valve-spindle  prevents  leakage  of  fluid.     In  this  valve  the  seat 


J=^ 


SL 


Fig.  ioo. 

is  rounded,  and  the  valve  face  is  a  ring  of  a  peculiar  composi- 
tion, let  into  the  valve  at  R.  When  the  valve  is  shut,  this 
composition  is  squeezed  down  onto  the  seat  and  makes  a 
tight  joint. 

If  the  fluid  enters  the  valve  from  the  right-hand  side,  the 


2=54 


STEAM-BOILERS. 


valve-spindle  may  readily  be  packed  to  prevent  leakage  while 
the  valve  is  closed.  If  the  fluid  entered  the  valve  at  the 
other  end,  it  would  be  necessary  to  shut  off  the  fluid  from 
the  entire  pipe  in  order  to  pack  the  valve. 

Angle-valves. — This  form  of  valve,  shown  by  Fig.  100, 
has  an  inlet  at  the  bottom  and  an  outlet  at  one  side,  It  may 
take  the  place  of  an  elbow  at  a  bend  in  piping.  The  valve 
is  made  in  two  parts.  The  upper  part  carries  a  ring  of  soft 
metal  which  forms  the  bearing-surface.  The  lower  part  has 
ribs  or  wings  which  enter  the  opening  through  the  valve-seat 
and   guide   the  valve  to  its  seat.      The   valve-spindle   has   a 


Fig.  iwi. 


sorew  at  the  upper  end  which  passes  through  a  yoke  entirely 
Outside  of  the  body  of  the  valve. 

The  body  of  the  valve  is  made  of  cast  iron.      The  valve, 


BOILER   ACCESSORIES. 


2  55 


valve-seat,  valve-spindle,  and  stuffing-box  follower  are  made 
of  brass  or  composition. 

This  form  ot  valve  is  frequently  used  tor  the  stop-valve 
between  the  boiler  md  the  main  steam-pipe. 

Straightway  or  Gate  Valve. — This  form  of  valve  gives 
a  straight  passage  through  the  valve,  and  offers  very  little 
resistance  to  the  flow  of  fluids  when  it  is  open.  Fig.  101 
represents  a  Chapman  valve,   in  which  the  valve  is  wedge- 


FlG. 


shaped  and  is  forced  against  a  wedge-shaped  seat.  The  valve- 
spindle  is  held  at  a  fixed  height  by  a  collar,  and  draws  up  or 
forces  down  the  valve  to  open  or  close  it.  The  body  of  the 
valve  is  of  cast  iron  ;  the  valve,  valve-spindle,  and  stuffing-box 
are  ot  brass-,  the  valve-seat  is  a  soft  composition. 

Fig.  102  represents  a  Peet  valve,  which  has  the  faces  of  the 
valve-seats  parallel.      The  valve  itself  is  made  in  two  pieces, 


*.S6 


STEAM-BOILERS. 


between  which  is  a  peculiar  casting,  U  shaped  at  the  bottom 
and  with  wedge-shaped  lips  at  the  top.  When  the  valve  is 
shut  this  casting  rests  on  the  bottom  of  the  valve  body,  and 
the  two  halves  of  the  valve  are  thrown  against  the  parallel 
valve-seats  by  the  wedge-shaped  lips  of  the  casting.  When 
the  valve  is  opened  this  casting  hangs  between  the  two  halves 
of  the  valve  by  the  under  side  of  the  wedge-shaped  lips. 

Check-valves  allow  fluids  to  pass  in  one  direction,  but 
not  in  the  other.      Fig.  103  represents  a  lift  check- valve;  i' 


Fig.  103. 


Fig.  104. 


resembles  a  globe  valve  without  a  valve-spindle.  Fluid 
entering  at  the  left  will  lift  the  valve  and  pass  out  at  the 
right.  Should  the  current  be  reversed  the  valve  will  be 
promptly  closed. 

Fig.  104  represents  a  swing  check-valve.  It  offers  less 
resistance  to  the  flow  of  fluid  than  the  valve  shown  above, 
and  there  is  less  chance  that  foreign  matter  will  lodge  on  the 
valve-seat.  The  valve  has  some  looseness  where  it  is  fastened 
to  the  swinging  arm,  so  that  it  may  properly  seat  itself. 

A  feed-pipe  must  always  have  a  check-valve  to  keep  the 
boiler-pressure  from  acting  on  tne  pump,  or  injector,  when  it 
is  not  at  work.  It  automatically  opens  to  allow  water  to  pass 
into  the  boiler.  There  should  also  be  a  stop-valve  (a  globe  or 
gate  valve)  near  the  boiler  which  can  be  shut  at  will;  thus 
when  the  check-valve  shows  signs  of  leaking  the  stop-valve 


BOILER    ACCESSORIES. 


2.S7 


may  be  shut,  and  then  the  check-valve  may  be  opened  and 
examined. 

Safety-valves  are  intended  to  prevent  the  pressure  oi 
steam  from  rising  to  a  dangerous  point.  In  order  to  accom- 
plish this,  the  effective  opening  of  the  valve  should  be  suffi- 
cient to  discharge  all  the  steam  that  the  boiler  can  make 
when  urged  to  its  full  capacity.  The  effective  opening  is 
equal  to  the  circumference  of  the  valve-seat  multiplied  by  the 
lift  of  the  valve,  if  the  valve-seat  is  flat;  if  the  valve-seat  is 
conical,  the  lift  should  be  measured  at  right  angles  to  the 
seat.  Then  if  /is  the  vertical  lift  and  if  a  is  the  angle  which 
the  seat  makes  with  the  vertical,  the  effective  lift  is 

/  sin  a. 

The  lift  of  a  safety-valve  rarely  exceeds  r/io  of  an  inch. 
A  two-inch  pop  safety-valve,  made  by  the  Crosby  Gauge  and 
Valve  Co.,  and  tested  at  the  laboratory  of  the  Massachusetts 
Institute  of  Technology,  was  found  to  lift  from  0.07  to  0.08 
of  an  inch.  The  valve  had  a  conical  seat  with  an  angle  of 
450.  The  actual  flow  was  about  95  per  cent  of  the  calculated 
flow  for  this  valve. 

The  amount  of  steam  that  a  boiler  can  make  may  be 
estimated  from  the  grate-area,  the  rate  of  combustion,  and  the 
evaporation  per  pound  ot  coal.  Tne  first  item  is  fixed,  and 
the  other  two,  though  somewhat  indefinite,  may  be  estimated 
from  the  type  of  boiler  and  the  conditions  under  which  it 
works. 

For  example,  a  factory  boiler  having  a  grate  5  feet  by  6 
feet  may  be  assumed  to  burn  18  pounds  of  coal  per  square 
foot  of  grate-surface  per  hour,  and  to  evaporate  8  pounds  of 
water   per  pound  of  coal.      It  will  therefore  generate 

5X6X18X8 

—  -7 — — — ^ —    -  =  1.2  pounds  of  steam  per  second. 
60  X  00  ' 

The  amount  of  steam  which  will  be  delivered  by  a  safety- 


258  STEAM  BOILERS. 

valve  may  be  calculated  by  an  empirical  equation  proposed 
by  Rankine ;   it  may  be  written 

70' 

in  which  W  is  the  weight  of  steam  in  pounds  delivered  per 
second,  A  is  the  effective  area  of  discharge  in  square  inches, 
and  p  is  the  absolute  pressure  of  the  steam  in  pounds  per 
square  inch. 

If  the  weight  of  steam  to  be  discharged  per  second  is 
known,  then  this  equation  may  be  used  to  calculate  the 
effective  area;   and  will  then  read 

70 IV 


A 


P 


In  the  example  given  above  the  weight  of  steam  per  second 
is  1.2  pounds.  If  the  steam-pressure  is  100  pounds  absolute 
(85.3  by  the  gauge),  then  the  effective  area  must  be 

,        7°  X  1.2 

A  =  —  =  0.84 

100 

of  a  square  inch.      If  the  effective  lift  be  assumed  to  be  0.075 
of  an  inch,  the  circumference  of  the  valve-seat  should  be 

0.84  -^  0.075  =  ii-2  inches, 

and  the  diameter  should  be  3.5  inches. 

A  common  rule  requires  that  there  shall  be  an  area  of  1/3 
of  a  square  inch  through  the  valve-seat  for  each  square  foot 
of  grate-surface.  It  so  happens  that  this  rule  gives  almost 
identically  the  same  result  as  that  just  calculated  for  the  above 
example;  thus: 

5  X  6 


10  square  inches, 
3 


\/ 


4  X  10  ,    .     , 

-  =  3.5  -j-  inches,  diameter. 


BOILER     ACCESSORIES. 


259 


This  rule  will  apply  only  to  a  certain  rate  of  coal  consump- 
tion: 15  to  20  pounds  per  hour  per  square  foot  of  grate  or  130 
to  160  pounds  of  steam  made  per  hour  from  a  square  foot  of 
grate. 

The  method,  given  on  the  preceding  page,  wherein  the  actual 
amount  of  steam  made  is  considered,  is  the  only  correct  method 
of  calculating  the  size  of  a  safety-valve. 

Lever  Safety-valve. — The  general  arrangement  and  some 
of  the  details  of  a  well-made  safety-valve  are  show/i  by  Fig. 


10: 


Fig.  105. 

The  body  of  the  valve  is  of  cast  iron,  and  has  an  opening 
at  one  side  from  which  the  escaping  steam  is  led  out  of 
the  boiler-room  through  an  escape-pipe.  The  valve  and 
valve-seat  are  of  brass  or  composition;  the  bearing-surface  is 
at  an  angle  of  45°  with  the  vertical.  The  load  is  applied  by 
a  steel  spindle,  to  a  point  beneath  the  bearing-surface  so  that 
the  valve  is  drawn  down  to  its  seat.  The  spindle  passes 
through  a  brass  ring  in  the  cover  to  the  valve-casing.  The 
load  is  applied  by  a  lever  with  a  fulcrum  at  A  and  a  weight 
at  D.  It  is  steadied  by  guides  cast  on  the  cover  of  the 
casing;  in  the  figure  the  valve  and  body  are  shown  in  section 
but  the  spindle,  lever,  guides  and  weight  are  shown  in  eleva- 
tion. 

It  is  important  that  the  pins  at  A  and  B  shall  be  loose  in 
their  bearings,   and   that   the  spindle   shall  be  free   where  it 


260  STEAM-BOILERS. 

passes  through  the  top  of  the  valve-case,  so  that  the  valve  may 
not  fail  to  rise  even  if  the  working  parts  are  rusted  a  little. 

After  a  safety-valve  has  blown  off  it  is  liable  to  leak  a 
little,  and  such  leakage  is  likely  to  injure  the  bearing-surface. 
In  this  way  safety-valves  sometimes  get  leaky  and  trouble- 
some. The  proper  way  is  to  regrind  the  valve  and  make  it 
tight,  but  if  the  boiler  attendant  is  careless  he  may  try  to 
stop  the  leak  by  jamming  the  valve  on  its  seat.  This  may 
be  done  bv  hanging  on  extra  weight,  or  wedging  a  piece  of 
wood  or  metal  against  the  lever.  To  remove  temptation,  it 
is  well  to  have  the  guides  for  the  lever  open  at  the  top,  and 
also  to  cut  off  the  lever  to  just  the  proper  length  so  that  the 
weight  cannot  be  slid  farther  out.  A  short  lever  and  a  heavy 
weight  are  better,  for  this  reason,  than  a  lighter  weight  and  a 
longer  lever. 

In  order  to  make  a  calculation  of  the  pressure  at  which  a 
safety-valve  will  blow  off,  we  must  know  the  diameter  of  the 
valve,  the  weight  of  the  valve  and  valve-spindle,  the  length 
of  the  lever  and  the  weight  hung  at  its  end,  and  the  weight 
and  centre  of  gravity  of  the  lever.  This  last  may  be  found 
by  calculation,  or  more  simply  by  balancing  the  lever  on  a 
knife-edge. 

In  the  example  shown  by  Fig.  105  the  valve  has  a  diameter 
of  5  inches  and  an  area  of 

3.1416  X  52  s 

*—± -i  =  19.635 

square  inches,  on  which  the  steam  presses. 

The  valve  and  spindle  weigh  15  pounds;  this  is  applied 
directly  at  the  valve.  The  weight  of  115  pounds  at  the  end 
of  the  lever,  is  56  inches  from  the  fulcrum  at  A.  It  is  equiva- 
lent to  a  weight  of 

— t £_  =  1610 


BOILER    ACCESSORIES.  26 1 

pounds  at  the  valve.  The  weight  of  the  lever  is  42  pounds, 
applied  at  the  centre  of  gravity  C,  20  inches  from  the  fulcrum. 
It  is  equivalent  to  a  weight  at  the  valve  of 

42  X  20 
=  210 

4 

pounds.  The  total  equivalent  weight,  or  the  load  on  the 
valve,  is 

15 -j-  1610  +  210=  1  S3 5  pounds. 

Since  the  area  of  the  valve  is  19.635  square  inches,  the 
steam-pressure  per  square  inch  required  to  lift  the  valve  will 
be 

1835  -r-  19.635  =  93.46  pounds. 

Problems  concerning  the  loading  of  a  safety-valve  may  be 
conveniently  stated  and  solved  by  taking  moments  about  the 
fulcrum  ;  that  is,  by  multiplying  each  weight  or  force  by  its 
distance  from  the  fulcrum. 

Let  the  weights  of  the  valve,  spindle,  lever,  and  weight 
be  represented  by  V,  S,  L,  and  W.  Let  a  be  the  distance  of 
the  weight  from  the  fulcrum  and  b  be  the  distance  from  the 
fulcrum  to  the  valve,  while  c  is  the  distance  of  the  centre  of 
gravity  of  the  lever  from  the  fulcrum. 

The  moment  of  the  weight  is  Wa,  and  the  moment  of  the 
lever  is  Lc.  The  moment  of  the  valve  and  spindle  is  {]" -\-S)b. 
All  three  moments  act  downward,  and  their  total  effect  is  equal 
to  their  sum, 

Wa  +  Lc  +  {V+S)b. 

If  the  diameter  of  the  valve  is  d,  then  the  area  is  ^nd2. 
Representing  the  steam-pressure  above  the  atmosphere  by/, 
the  force  acting  on  the  valve  is 

nd% 

— "' 


262  STEAM-BOILERS. 

and  the  moment  of  that  force  is 

nd%   , 

—  pb. 
4 

This  moment  acts  upward  and,  when  the  valve  lifts,  will 
be  equal  to  the  total  downward  moment.  So  that  the  equa- 
tion for  calculating  the  load  on  a  lever  safety-valve  is 

pb—  =  Ua  +  Lc  +  (T+  S)b. 

This  equation  gives  for  the  steam-pressure  at  which  the 
valve  shown  by  Fig.  89  will  lift 


P  = 


4\_Wa  +  Lc+(V-S)b-] 


7T 


dlb 


_  4(115  X  56  +  42  X  20+  15X4) 
•''p-  3.1416X  52X,4 

. •.  p  =  93.46  pounds, 

as  found  by  the  previous  calculation. 

For  a  second  example  let  us  find  the  distance  at  which 
the  weight  of  the  valve  shown  by  Fig.  105  must  be  placed 
from  the  fulcrum  in  order  that  the  valve  will  blow  off  at  50 
pounds  above  the  atmosphere. 

Solving  the  general  equation  for  a,  we  have 

■nd"1 
pb- Lc  -  (V+S)b 

A. 


w 

3.1416 

50  X  4  X  ^-7—  X  5   " 
4 
a  = 

-  42  X  20  — 

15  X  4 

115 

•.   a  =  26.32  inches. 


BOILER  ACCESSORIES.  26? 

For  a  third  example  find  the  weight  which  should  be  hung 
at  the  end  of  the  lever  if  the  valve  is  to  blow  off  at  30  pounds 
above  the  atmosphere. 

Here  we  have 


W 


W 


pb Lc  —  (V+S)b 


30  X  4  X  —      -  X5    -42X20-15x4 


56 


W =  26  pounds. 


These  last  two  problems  can  of  course  be  stated  and 
solved  much  after  the  first  manner  applied  to  the  first  problem, 
but  the  work,  which  will  amount  in  the  end  to  the  same 
thing,  cannot  be  so  well  arranged  nor  so  easily  done. 

Pop  Safety-valve.  —  A  defect  of  the  common  lever 
safety-valve  is  that  it  does  not  close  promptly  when  the 
steam-pressure  is  reduced,  and  it  is  apt  to  leak  after  it  has 
returned  to  its  seat. 

The  valve  shown  by  Fig.  106  has  a  groove  turned  in  the 
flange  which  projects  beyond  the  bearing-surface,  and  there  is 
another  groove  between  the  outer  edge  of  the  valve-seat  and  a 
ring  which  is  screwed  onto  the  valve-seat.  When  the  valve 
lifts  the  escaping  steam  is  twice  deflected,  once  by  the  groove 
in  the  valve  and  again  by  the  groove  at  the  valve-seat.  The 
reaction  of  the  steam  assists  the  pressure  of  the  steam  on  the 
under  surface  of  the  valve,  and  suddenly  opens  the  valve  to 
its  full  extent.  The  valve  stays  wide  open  till  the  steam- 
pressure  in  the  boiler  has  fallen  a  few  pounds  below  the  blow- 
ing-off  pressure,  and  then  the  valve  shuts  as  suddenly  as  it 
opens. 

The  ring  which  is  screwed  onto  the  valve-seat  has  a  number 


264 


STEAM-BOILERS. 


of  holes  drilled  through  it  to  allow  steam  to  escape  from  the 
groove  at  its  upper  surface.      It  may  also  be  screwed  up  or 


Fig.  106. 


down  to  adjust  its  position;  a  screw  at  the  side  of  the  case 
clamps  it  when  adjusted.     The  action  of  the  valve  is  regulated 


BOILER  ACCESSORIES.  265 

by  the  number  of  holes  in  the  ring  and  by  its  vertical  posi- 
tion. 

This  valve  is  loaded  by  a  helical  spring.  The  tension  of 
the  spring  and  the  load  on  the  valve  is  regulated  by  a  sleeve 
which  is  screwed  down  through  the  top  of  the  valve-case.  It 
is  of  course  possible  to  load  a  plain  safety-valve  in  a  similar 
way,  or  to  load  a  pop-valve  with  a  lever  and  weight.  The 
valve  is  extended  up  in  the  form  of  a  thin  shell  to  guard  the 
spring  from  the  escaping  steam.  The  valve-spindle  is  ex- 
tended through  the  top  of  the  case,  and  may  be  pulled  up 
by  a  lever  when  it  is  desired  to  ease  the  valve  off  from  its 
seat.  A  drip  at  the  lower  right-hand  side  of  the  case  draws 
off  water  which  may  collect  in  the  case. 

The  valve  and  its  seat,  the  adjusting-ring  on  the  seat,  the 
valve-spindie,  and  the  bearing-pieces  on  the  spring  are  all 
brass.  There  is  also  a  brass  ring  inside  the  shell  that  extends 
down  from  tne  cover  and  incloses  the  spring.  There  should 
be  a  little  clearance  between  this  brass  ring  and  the  shell  on 
the  valve  so  that  the  valve  shall  not  be  cramped.  The  entire 
valve-casing,  which  is  made  in  four  parts,  is  of  cast  iron. 

It  is  evident  that  the  annular  space  between  the  bearing- 
surface  and  the  edge  of  the  groove  of  the  valve  in  Fig.  106  is 
subjected  to  a  pressure,  when  the  valve  is  open,  which 
depends  on  the  rates  of  flow  to  and  from  this  space.  Some 
pop-valves  depend  mainly,  if  not  wholly,  on  such  an  additional 
pressure  for  their  action,  and  it  is  claimed  by  some  makers 
that  all  pop-valves  do.  The  closeness  of  regulation  by  a  pop- 
valve  may  be  controlled  by  determining  the  width  of  the  an- 
nular space  and  by  adjusting  the  grooved  ring  outside  the 
valve-seat.  Valves  have  been  made  with  only  two  pounds 
for  the  range  of  pressure  between  opening  and  closing;  thus, 
a  pop-valve  may  open  at  100  pounds  pressure  and  close  at  98 
pounds. 

A  safety-valve  should  be  set  by  trial,  to  blow  off  at  the 
required  pressure  as  shown  by  a  correct  steam-gauge.  A 
safety-valve   should    occasionally  be    lifted    from    its    seat  to 


2 56  STEA  M  BOILERS. 

insure  that  it  is  in  proper  condition.  An  unexpected  opening 
of  a  safety-valve  or  continued  leakage  shows  lack  of  attention 
to  duty  on  the  part  of  boiler  attendants.  While  the  safety- 
valve  for  a  boiler  should  be  able  to  deliver  all  the  steam  it  can 
make,  it  may  be  considered  that  the  proper  function  of  a 
safety-valve  is  to  give  warning  of  excessive  pressure.  The 
safety  of  the  boiler  must  always  depend  on  the  faithfulness 
and  intelligence  of  the  boiler  attendants. 

The  discharge  of  a  safety-valve  is  often  piped  outside  the 
boiler-room.  Such  pipes  should  be  dripped  to  keep  them  free 
of  water.     Each  safety-valve  should  be  piped  out  doors  separately. 

Water-column. — The  position  of  the  water-level  in  a 
boiler  is  indicated  either  by  a  water-glass  or  by  gauge-cocks  or 
by  both.  These  may  be  connected  directly  to  the  front  end 
of  the  boiler,  or  they  may  be  placed  on  a  fitting  known  as  a 
ivater-column  or  combination.  Fig.  107  shows  a  good  form  of 
water-column.  It  is  a  cast-iron  cylinder  connected  to  the 
steam  space  at  the  top  and  to  the  water-space  near  the 
bottom.  The  normal  position  of  the  water-level  is  near  the 
middle.  There  is  at  the  bottom  a  globular  receiver  into 
which  deposits  from  the  water  may  settle  and  be  blown  out 
at  will.  # 

In  one  side  of  the  water-column  are  brass  fittings  for  the 
water-glass,  which  is  a  strong  tube  of  special  make.  The 
glass  tube  passes  through  a  species  of  stuffing-box  in  the  brass 
fitting.  The  joint  is  made  tight  by  a  rubber  ring  which  fits 
on  the  tube  and  is  compressed  by  a  follower  screwed  onto  it. 
Each  fitting  has  a  valve  by  which  steam  may  be  shut  off  when 
the  tube  is  cleaned  or  replaced.  A  cock  at  the  bottom  drains 
water  from  the  tube;  for  this  purpose  the  lower  vah/e  is 
closed  and  the  cock  is  opened.  Stout  wires  at  the  side  of  the 
glass  tube  guard  it  from  injury. 

If  either  valve  leading  to  the  water-glass  is  closed,  the 
level  of  the  water  will  rise  in  the  tube.      If  the  upper  valve  is 


BOILER  ACCESSORIES. 


267 


closed,  the  steam  in  the  upper  part  of  the  tube  is  gradually 
condensed  by  radiation,  and  is  replaced  by  water  entering 
from  below.  If  the  lower  valve  is  closed,  the  condensation 
of  steam  from  radiation  will  accumulate  and  gradually  fill  the 
tube. 

Gauge-glasses    are     very    brittle     and,    though    carefully 
annealed,  are  under  considerable  stress  from  unequal  cooling. 


Fig. 


107. 


Before  a  tube  is  put  in  it  may  be  cleaned  by  pouri.ig  acid 
through  it,  or  by  drawing  a  bit  of  waste  through  on  a  string. 
A  wire  should  never  be  forced  through  a  glass  tube,  for  the 
slightest  scratch  may  start  a  break  which  will  end  in  reducing 
the  tube  to  small  pieces.  When  a  tube  is  in  place  it  may  be 
cleaned  by  closing  the  lower  valve  and  opening  the  drainage- 
cock  and  allowing  steam  to  blow  through. 

When  a  boiler   is   left  banked   overnight    the  water-glass 


268  STEAM-BOILERS. 

should  be  shut  off,  since  a  breakage  may  result  in  drawing  the 
prater  in  the  boiler  down  to  the  level  of  the  lower  end  of  the 
tube. 

In  addition  to  the  water-glass,  which  shows  at  all  times  the 
level  of  the  water,  the  water-column  carries  three  gauge- 
cocks.  One  is  set  at  the  desired  water-level,  one  a  little 
above  and  one  a  little  below.  Steam  from  the  steam-space, 
through  the  upper  gauge-cock,  becomes  superheated  as  it 
blows  into  the  atmosphere  and  looks  blue.  The  lower  cock 
discharges  hot  water  from  the  water-space,  which  flashes  into 
steam  as  it  escapes,  but  it  has  a  white  color,  which  is  very- 
distinct  from  that  of  the  jet  from  the  steam-space.  A  good 
fireman  occasionally  tests  the  position  of  the  water-level  by 
using  the  gauges  to  be  sure  that  the  indication  by  the  water- 
glass  is  not  erroneous.  Engineers  on  locomotives,  and  boiler 
attendants  where  very  high-pressure  steam  is  used,  often 
prefer  to  depend  entirely  on  the  gauge-cocks,  and  dispense 
with  the  water-glass,  which  may  be  annoying  or  dangerous 
when  it  breaks. 

The  water-column  shown  by  Fig.  107  has  an  alarm-whistle, 
which  shows  above  the  main  casting,  at  the  right.  It  is  con- 
trolled by  two  floats  inside  the  cylinder;  one  float  at  the  top 
opens  the  valve  leading  to  the  whistle  when  the  water-level 
is  too  high,  the  other  near  the  bottom  blows  the  whistle  when 
the  water-level  is  too  low. 

If  the  fire  is  stirred  up  under  a  boiler  which  has  had  the 
fire  banked,  the  water-level  rises  in  the  water-glass;  the 
reason  being  that  the  circulation  is  from  the  front  of  the  boiler 
to  the  rear,  and  that  this  circulation  is  maintained  by  a  differ- 
ence of  level  between  the  front  and  rear  ends.  On  the  con- 
trary, the  water-level  falls  when  a  boiler  which  has  been 
steaming  freely  is  checked. 

Steam-gauges. — The  pressure  of  the  steam  in  a  boiler  is 
shown  by  a  steam-gauge  constructed,  as  shown  by  Figs.  108, 
109,  and  no.     The  essential  part  is  a  flattened  brass  tube  b^nt 


BOILER    ACCESSORIES  269 

into  the  arc  of  a  circle  as  shown  by  Fig.  108.  The  section  of  the 
tube  may  be  an  oval,  or  it  may  have  two  longitudinal  corrugations 
as  shown  by  Fig.  109. 

Pressure  inside  of  such  a  tube  makes  it  bulge  and  tends 
to  straighten  it.      One  end  is  fixed  and  is  in  communication 


Fig.  108.  Fig.  109. 

with  the  space  where  the  pressure  is  to  be  measured.  The 
other  end  is  closed  and  is  free  to  move.  It  is  connected  by 
a  link  to  a  lever  which  bears  a  circular  rack  in  gear  with  a 
pinion.  The  motion  of  the  free  end  of  the  tube  is  multiplied 
and  is  shown  by  the  motion  of  a  needle  on  the  pinion.  The 
scale  on  the  dial  is  marked  by  trial  to  agree  with  the  indica- 
tions of  a  mercury  column  or  of  a  standard  gauge.  A  hair- 
spring on  the  pinion  (not  shown  in  Fig.  108)  takes  up  the  back- 
lash of  the  multiplying-gear. 

The  long,  flexible  spring-tube  is  liable  to  vibrate  to  an 
undue  extent  when  the  gauge  is  exposed  to  the  jarring  of  a 
locomotive.  To  avoid  this  difficulty,  two  short  stiffer  tubes 
have  their  ends  connected  to  a  more  effective  multiplying 
device,  shown  by  Fig.  no.  The  greater  number  of  joints  in 
this  device  makes  it  less  sensitive  than  the  other  form. 

Since  the  spring-tube  changes  its  shape  if  the  temperature 
changes,  hot  steam  should  not  be  allowed  to  enter  it.      An 


270 


STEAM-BOILERS. 


inverted  siphon  or  U  tube  filled  with  water  is,  therefore,  inter- 
posed  between  the  gauge  and  the  steam  from  the  boiler. 


Fig.  no. 
Safety-plugs,  or  Fusible  Plugs,  as  shown  bv  Fig.  in,  are 
made  of  brass  and  provided  with  a  core  of  fusible  metal.  If 
the  plate  into  which  they  are  screwed  is  in  danger  of  over- 
heating, the  fusible  metal  will  melt  and  run  out,  and  steam 
and  water  will  blow  into  the  furnace.  If  the  fire  is  not  put 
out,  it  will  at  least  be  checked  and  the  attention  of  the  fire- 
man will  be  attracted. 

The  melting-point  of  fusible  metals  is  not  always  certain, 
and  the  plugs  not  infrequently  blow  out  when  there  is  no  ap- 
parent cause.  On  the  other  hand,  they  sometimes  fail  to  act 
when  the  plate  is  overheated.  If  the  plug  is  covered  with  incrus- 
tation, the  fusible  metal  may  run  out  without  giving  warning. 
The  following  are  some  of  the  places  where  a  fusible  plug 
is  used : 

In  the  back  head  of  a  cylindrical  tubu- 
lar boiler,  about  three  inches  above  the 
top  row  of  tubes. 

In    the    crown-sheet    of    a    locomotive 
|J  fire-box. 

— ';  In   the   lower   tube-sheet   of    a   vertical 

Mil|_  boiler;   or  sometimes  in   one  of  the  tubes  a 

Fig.  hi.  little  above  that  tube-sheet. 


BOILER    ACCESSORIES. 


271 


In  the  lower  side  of  the  upper  drum  of  a  water-tube 
boiler. 

The  fusible  composition  has  a  conical  form  so  that  it  can- 
not be  blown  out  by  the  pressure  of  the  steam. 

Foster  Reducing-valve. — When  steam  is  desired  at  a 
less  pressure  than  that  of  the  boiler,  it  is  passed  through  a 
reducing-valve  like  that  shown  by  Fig.  112.  The  valve  //is 
held  open  by  the  spring  at  J,  acting  through  the  toggle-levers 


T^^J 


Fig.  112. 

a,  until  the  steam-pressure  in  the  exit-pipe  B,  pressing 
on  the  diaphragm  D,  is  able  to  overcome  the  spring  and 
close  the  valve.  The  pressure  at  which  this  may  occur  is 
determined  by  the  tension  of  the  spring,  which  may  be 
regulated  by  the  screw  at  K.  It  is  expected  that  the 
valve  will  be  drawn  up  so  as  to  admit  just  the  proper 
amount  of  steam  to  the  exit-pipe  B  to  maintain  the  de- 
sired pressure  in  it.  Valves  for  this  purpose  are  liable  to 
work    intermittently,    i.e.    they    close    till    the    pressure    falls 


272 


STEAM-BOILERS. 


below  the  proper  point,  then  they  open  and  raise  the  steam- 
pressure  above  that  point.  The  valve  is  a  species  of  throt- 
tling-valve,  and  therefore  cannot  be  expected  to  remain  tight. 
If  the  machinery  supplied  by  the  reducing-valve  is  liable  to 
be  injured  by  excessive  pressure,  there  must  be  a  stop-valve 
beyond  the  reducing-valve.  The  stop-valve  must  be  closed 
when  no  steam  is  drawn,  and  must  be  used  to  regulate  the 
supply  of  steam  until  the  amount  drawn  exceeds  the  leakage 
of  the  reducing-valve. 

As  practically  all  reducing-valves  make  use  of  a  diaphragm, 
or  a  spring,  they  all  must  give  out  after  a  certain  number  of  vibra- 
tions of  the  spring  or  diaphragm.  When  a  reducing-valve  gives 
out  there  is  invariably  full  pressure  established  beyond  the  reduc- 
ing-valve. A  safety-valve  large  enough  to  take  care  of  the 
capacity  of  the  pipe  should  be  placed  beyond  the  reducing-valve. 

If  high-pressure  and  low-pressure  boilers  deliver  into  one 
main  there  must  be  on  the  low-pressure  main  safety-valves  large 
enough  to  take  care  of  all  the  steam  made  by  the  high-pressure 
boilers. 

The  Damper-regulator  shown  by  Fig.  113  places  the 
damper  in  the  flue  leading  to  the  chimney  under  the  control 
of  the  steam-pressure,  so  that  if  the  pressure  of  the  steam  falls, 
the  damper  is  opened  wider  to  quicken  the  fire.  The  pressure 
of  the  steam  in  the  boiler  is  communicated  through  the  pipe  a 
to  the  lower  surface  of  a  diaphragm,  and  lifts  the  loaded  lever  b, 
which  stands  half-way  between  the  stops  at  the  middle  of  its 
length  when  the  steam-pressure  is  at  the  proper  point.  Should 
the  steam-pressure  rise  above  the  proper  point,  it  raises  the  lever 
and  opens  a  small  piston-valve  at  c,  and  water  from  a  hydrant 
flows  into  d  and  presses  on  a  piston  which  lifts  the  weights  at  e 
and  so  shuts  the  damper.  The  weighted  head  e  of  the  piston  is 
connected  by  a  chain  to  the  lever/,  and  closes  the  valve  c  as  it 
rises,  and  so  shuts  off  the  water  from  the  hydrant. 

If  the  pressure  in  the  boiler  drops  the  lever  b  as  it  descends 


BOILER    ACCESSORIES. 


2  73 


pulls  down  the  piston-vaive  in  c  far  enough  to  open  a  dicsharge- 
port,  which  allows  the  water  under  the  piston  in  d  to  flow  to  waste. 
The  weights  at  e  are  made  heavy  enough  to  overhaul  the 
damper  and  to  overcome  the  piston  friction  in  d. 


Fig.  113, 


The  diameter  of  the  brass  pipe  d  is  fixed  by  the  water-pressure 
available  for  working  the  regulator. 

Should  the  water-pressure  fail,  the  regulator  would  not  operate 
and  the  damper  would  be  held  open. 

Oftentimes  damper-regulators  are  supplied  with  water  from 
the  fire-tanks  located  on  the  roofs  of  many  of  our  factories. 

A  regulator  of  the  same  form  attached    to    a   throttle-valve 


274 


STEAM-BOILERS. 


acts  as  a  reducing-valve,  and  regulates  the  pressure  below  the 
valve  with  a  variation  of  less  than  one  pound.     Fig.  114  shows 

the  steam-valve  used  when  the- 
Locke  regulator  acts  as  a  reducing- 
valve.  The  valve  is  a  double 
valve  which  is  nearly  balanced, 
but  with  a  slight  tendency  to  rise 
under  steam-pressure,  as  the  lower 
valve  is  the  larger.  The  cylin- 
drical part  of  the  valve  is  cut  into 
V  notches,  so  that  the  supply  of 
steam  is  regulated  to  a  nicety  when 
the  valve  is  partially  open.  The 
cylindrical  portion  of  the  valve 
protects  the  valve-seat  and  the 
valve-face  so  that  the  valve  may  remain  tight  when  closed. 

Steam-traps. — The  object  of  a  steam-trap  is  to  drain  con- 
densed water  from  steam-pipes  without  allowing  steam  to  escape. 
As  a  rule  a  trap  is  placed  below  the  pipe  to  be  drained  so  that 
the  drip  from  the  pipe  will  run  into  it.  Some  traps  that  return 
the  condensed  water  to  the  boiler  do  not  conform  to  this  rule. 

Some  traps,  such  as  the  McDaniels,  the  Baird,  and  the 
Walworth,  have  a  valve  under  the  control  of  a  float,  which 
will  allow  water  to  pass  but  not  steam. 

A 


Fig.  114. 


Fig.   115. 
The  McDaniels  trap  is  shown   by   Fig.  115.       The    drip 
enters  at  C  and  escapes  through  the  exit  at  E  when  the  valve 


BOILER    ACCESSORIES. 


275 


G  is  open.  This  valve  is  raised  by  the  spherical  float  when 
the  water  rises  to  a  sufficient  height.  When  the  water  is 
drained  from  the  pipe  served  by  the  trap,  the  water-level  in 
the  trap  falls  and  the  valve  G  is  closed.  D  is  a  countei- 
weight  to  balance  the  weight  of  the  spherical  float.  The 
valve  at  G  can  be  opened  by  screwing  down  the  screw  at  A 


Fig.  "7- 
on  to  the  counterweight.      The  trap  can  be  emptied  through 
the  valve  at  F. 

The  Baird  trap,  Fig.  116,   has  a  spherical  float  D  which 


276 


STEAM-BOILERS. 


controls  a  piston-valve  at  J.  The  inlet  is  at  C,  and  the  outlet 
at  /.  The  screws  A  and  B  allow  the  valve  J  to  be  opened  or 
closed  by  hand. 

The  Walworth  trap  (Fig.  117)  has  a  floating  bucket  into 
which  the  drip  overflows  after  the  outer  case  is  partially 
filled.  When  the  bucket  sinks  it  opens  a  passage  through 
the  central  spindle,  and  the  water  in  the  bucket  is  driven  cut 
through  this  spindle.  The  hand-wheel  and  screw  at  the  tcp 
control  a  valve  which  is  closed  when  the  trap  is  working. 

The  Flynn  trap  (Fig.  118)  depends  for  its  action  on  a  head 
of  water  acting  on  a  flexible  diaphragm.  Water  may  enter 
at  the  top  or  the  bottom  at  ori- 
fices marked  A.  It  fills  the  pipe 
B  and  the  globe  C  as  high  as 
the  end  of  the  pipe  E,  and  pro- 
duces a  pressure  of  about  a 
pound  per  square  inch  on  the 
under  side  of  the  diaphragm  at 
D.  The  spring  at  G  produces 
a  pressure  of  about  half  a  pound 
per  square  inch  on  the  upper 
side  of  the  diaphragm.  Conse- 
quently the  valve  leading  from 
the  chamber  F  to  the  escape- 
pipe  H  is  closed  so  long  as  the 
pipe  E  remains  empty.  But 
when  the  water  overflows  the 
top  of  the  pipe  E  and  fills  the 
chamber  F,  the  water-pressure 
on  top  of  the  diaphragm  will  be 
the  same  as  that  on  the  bottom, 
and  the  spring  at  G  will  open 
the  valve  and  allow  water  to 
escape.  If  the  supply  of  water 
at  A  ceases,  the  pipe  E  will  be  emptied  and  the  valve  will  be 
closed  under  the  influence  of  the  pressure  on   the  under  side 


Fig.  11 


BOILER   ACCESSORIES. 


277 


OUTLET 
Fig.  119. 


of  the  diaphragm.      In  the  trap  as  actually  constructed   the 

pipe  E  is  about  28  inches  long  ;  in 
the  figure  it  is  made  shorter  in 
proportion. 

The  Curtis  trap  (Fig.  119)  has 
an  expansion-chamber  at  C  which 
[inlet  is  closed  by  a  diaphragm  A  at  the 
bottom,  and  is  filled  with  a  very 
volatile  fluid.  So  long  as  the  ex- 
pansion-chamber is  immersed  in 
water  the  pressure  of  the  fluid  on 
the  diaphragm  is  balanced  by  the 
spring  on  the  valve-spindle  B.  If 
the  water  is  drained  away  and  the 
chamber  is  exposed  to  the  temper- 
ature of  steam  (2120  F.  or  more),  the  fluid  vaporizes  and 
exerts  enough  pressure  on  the  diaphragm  to  compress  the 
spring  and  close  the  exit-valve. 

Return  Steam-trap.— The  traps  thus  far  considered  usu- 
ally discharge  against  the  pressure  of  the  atmosphere.  They 
may  discharge  into  a  closed  tank  against  a  pressure  that  is  higher 
than  the  atmosphere,  but  in  all  cases  the  pressure  in  the  pipes 
drained  by  the  trap  must  be  higher  than  the  discharge-pressure. 
Return  steam-traps  are  arranged  to  discharge  directly  into  the 
boiler. 

The  Bundy  return-trap,  shown  by  Fig.  120,  is  set  three  feet 
or  more  above  the  water-line  in  the  boiler.  It  is  so  made  that 
it  is  first  opened  to  the  pipe  to  be  drained,  and  fills  up 
under  the  pressure  in  that  pipe.  It  is  then  put  in  commu- 
nication with  the  steam-space  and  with  the  water-space  of 
the  boiler,  and  the  water  previously  collected  drains  into  the 
boiler. 

The  trap  consists  of  a  pear-shaped  receptacle  or  closed 
bowl,  hung  on  trunnions,  through  which  the  bowl  is  filled  and 
emptied.  When  empty  the  bowl  is  raised  by  a  weight  and 
lever;  when  filled  with  water  it  overbalances  the  weight  and 


278  STEAM-BOILERS. 

falls.  The  ring  around  the  bowl  limits  the  motion.  The 
condensed  water  from  the  pipe  or  system  of  pipes  to  be 
drained  enters  the  trap  through  the  check-valve  B,  which  pre- 
vents water  from  flowing  back  from  the  trap  into  the  pipe  to 
be  drained.  The  trap  is  emptied  through  the  check-valve  A, 
which  prevents  water  from  the  boiler  from  flowing  into  the 


Pig.  120. 


trap.  At  C  is  a  valve  under  the  control  of  the  trap,  which 
receives  steam  by  a  special  pipe  from  the  boiler.  When  the 
trap  is  empty  and  is  lifted  by  the  weight  and  lever,  the  valve 
C  is  thrown  down  and  is  shut ;  water  then  flows  in  through 
the  valve  B  from  the  pipe  to  be  drained,  and  air  escapes  from 
an  air-valve  below  C,  which  is  open  in  this  position  of  the 
trap.      A  check-valve  on  the  air-pipe  prevents  air  from  en- 


BOILER   ACCESSORIES. 


279 


tering  the  trap  if  a  vacuum  happens  to  be  formed  in  it.  When 
the  bowl  is  filled  it  falls  and  opens  the  steam-valve  C,  and 
steam  enters  the  bowl  through  a  curved  pipe  shown  in  Fig. 
120.  The  pressure  in  the  bowl  is  now  equal  to  that  in  the 
boiler,  and  the  water  collected  flows  into  the  boiler  by  gravity. 
Separators. — If  steam  is  carried  to  a  distance  in  pipes,  a 
considerable  amount  of  water  of  conden. 
sation  accumulates.  It  is  undesirable  to 
have  this  water  delivered  to  a  steam- 
engine  in  any  case,  but  if  the  water  ac- 
cumulates in  a  pocket  or  a  sag  in  the 
piping,  it  may  come  along  with  the  steam 
in  a  body  whenever  there  is  a  sudden 
change  of  steam-pressure,  and  then  the 
engine  will  be  in  danger  of  injury. 

A  good  way  of  removing  such  water 
is  to  allow  the  steam  to  come  to  rest 
in  a  steam-drum  of  suitable  size,  from 
which  the  water  is  drained  by  a  steam- 
trap;  the  steam  meanwhile  may  flow  from 
a  pipe  at  the  top  of  the  drum.  A  small 
steam-drum  used  as  separator  is  likely 
to  fail,  from  the  fact  that  the  steam  does 
not  come  to  rest,  or  because  the  entering 
and  leaving  currents  of  steam  are  not 
properly  separated. 

The    Stratton    separator,    shown     by 

Fig.   121,  brings  in  the  steam  at  one  side 

of   a   cylinder,    with    a    whirling    motion 

Fig.  i2i.  that  throws  the  water  onto  the   side   of 

the  cylinder;  dry  steam  escapes  through  a  pipe  in  the  middle. 

A  good  steam-separator  will  remove  all  but  one  or  two 

per  cent  of  moisture  from  steam,  even  though  the  entering 

steam  is  very  wet. 

Attention  has  already  been  called  to  the  use  of  separators 


280 


STEAM-BOILERS. 


with   some  forms  of  water-tube  boilers  which  do  not  have  a 
sufficient  free  water-surface  for  the  disengagement  of  steam. 

The  three  separators  shown  by  Figs.  122,  123,  and  124  may 
be  used  on  the  steam-pipe  to  separate  water  from  the  steam, 
or  on  the  exhaust-pipe  of  an  engine  to  collect  the  water  and  oil. 


Fig.  122. 


Fig.  123. 


Fig.  122  represents  the  Curtis  baffle-plate  separator.  The 
entering  steam  is  divided  into  three  portions,  which  flow  as  shown 
by  the  arrows. 

Water  or  oil  coming  in  contact  with  the  plates  adheres  to  the 
plates  and  is  collected  in  the  space  at  the  bottom. 

The  Triumph  separator,  shown  by  Fig.  123,  removes  oil  or 
water  by  centrifugal  action  and  by  a  settling-chamber.  The 
direction  of  flow  is  shown  by  the  various  arrows. 

Fig.  124  illustrates  the  Detroit  separator.  The  steam  is 
directed  against  a  corrugated  annular  plate  to  which  water  and 


BOILER    A  CC  'ESS(  1RIE.S. 


28l 


oil  adheres.   A  settling-chamber  in  the  shape  of  an  enlargement  of 
the  casting  allows  floating  particles  to  be  deposited  by  gravity. 

Tests  made  with  these  separators  connected  to  the  exhaust- 
pipe  of  an  engine  have  shown  that  by  their  use  80  per  cent  of  the 
cylinder  oil  used  in  the  engine  mav  be  taken  out  of  the  exhaust. 


Fig.  124. 

Most  of  this  oil  is  mixed  with  water  in  such  a  way  that  it  cannot 
be  separated  from  the  water. 

Oil-filters. — If  exhaust  steam  is  used  for  heating  and  the 
condensation  in  the  system  is  returned  as  feed-water  to  the  boiler 
it  is  of  great  importance  that  this  water  should  be  free  from  oil. 

An  oil-separator  will  take  out  80  per  cent  of  the  oil.  The 
greater  part  of  the  20  per  cent  remaining  may  be  taken  out  by 
a  straw-filter. 

The  returns  from  the  heating  system  are  passed  through  a 
box  about  8  feet  long  and  2  feet  square  in  section,  open  at  the 
top.  There  are  partitions  across  the  box  so  that  the  water  enter- 
ing at  one  end  flows  over  one  partition  and  under  the  next,  over 
the  third,  and  so  on. 

The  entire  box  is  filled  full  of  hay  or  straw.     Water  is  taken 


282 


STEAM-BOILERS. 


into  the  feed-pump  from  the  opposite  end  of  the  box.  If  this 
straw  is  changed  once  in  two  weeks,  or  oftener  if  necessary,  not 
enough  oil  will  get  into  the  boilers  to  cause  any  trouble. 

Feed-water  Heaters. — The  feed-water  supplied  to  a  boiler 

SAFETY 
VALVE 


BLOW 


EXHAUST 


FEED  TO 

BOILER 


FEED  FROM 
PUMP 


F5?!l^ia^ 


MUD   BLOW  OFF 

Fig.  125. 

♦nay  be  heated  up  to  the  temperature  of  the  exhaust-steam  by 

passing  it  through  a  feed-water  heater.      Feed-water  heaters 

are  sometimes  made  open,   i.e.,  the  steam  from  the  engine 


BOILER   ACCESSORIES. 


283 


mingles  with  and  heats  the  feed-water.  Such  heaters  have 
the  disadvantage  that  the  oil  from  the  engine  is  carried  into 
the  boiler. 

A  closed  feed-water  heater  resembles  a  surface  condenser, 
and  as  the  steam  and  water  do  not  mingle,  there  is  no  danger 
of  carrying  oil  from  the  engine  into  the  boiler.  The  Wain- 
wright  heater,  shown  by  Fig.  125,  has  the  heating-surface  of 
corrugated  copper  or  brass  tubes,  of  peculiar  make,  to  allow 
for  expansion.  The  steam  from  the  engine  passes  around 
the  tubes  and  the  feed-water  passes  through  the  tubes. 

The  Berryman  feed-water  heater,  shown  by  Fig.  126,  is 
arranged  to  have  the  exhaust-steam  pass 
through  a  series  of  inverted  U  tubes, 
around  which  the  feed-water  circulates. 
Live-steam  feed-water  heaters  take 
steam  from  the  boiler  to  raise  the  tem- 
perature of  the  feed-water  up  to,  or 
nearly  to,  the  temperature  in  the  boiler. 
The  principal  advantage  appears  to  be 
that  unequal  contraction,  due  to  the  in- 
troduction of  cold  water,  is  avoided.  It 
is  claimed  that  with  some  forms  of 
boilers  a  better  circulation  is  obtained 
by  aid  of  such  a  heater. 

The  use  of  a  feed-water  heater  for 
removing  lime-salts  from  feed-water  has 
been  discussed  on  page  73,  and  an  ex. 
ample  of  such  a  feed-water  heater  wa. 
illustrated  in  connection  therewith. 
Feed-pipes. — The  temperature  of 
r<M?T~  __  the   feed-water  is  usually  much  below 

Tjs^_UI — V     the  temperature  in  the  boiler.      It  thus 
becomes  essential  to  so  locate  the  inlet, 
and  to  so  distribute  the  water,  that  un- 
due local  contractions  may  not  occur;  this  is  of  special  im- 


MUD  PIPE 

Fig.   126. 


284  STEAM  BOILERS 

portancc  when  the  supply  is  intermittent.  The  feed-pipe  for 
the  cylindrical  tubular  boiler,  shown  by  Plate  I,  enters  die  shell 
near  the  water-iine,  through  the  front  head.  It  is  carried 
along  one  side  of  the  boiler  for  about  three  fourths  of  its  length, 
and  then  is  carried  across  over  the  tubes  and  opens  downward. 
A  feed-pipe  is  often  perforated  to  give  a  better  distribution  of 
the  feed-water. 

The  shell  is  reinforced  by  a  piece  of  plate  riveted  on  the 
outside,  where  the  feed-pipe  enters  the  boiler.  The  end  of 
the  pipe  has  a  long  thread  cut  on  it,  so  that  it  can  be  secured 
through  the  reinforcing-plate  and  the  boiler-shell,  and  may 
then  receive  a  pipe-coupling  which  connects  it  to  the  continu- 
ation of  the   feed-pipe  inside. 

Sometimes  the  feed-water  is  delivered  to  an  open  trough 
inside  the  boiler,  from  which  it  overflows  in  a  thin  sheet. 
Or  a  perforated  pipe  may  deliver  the  water  in  form  of  spray 
in  the  steam -space.  Either  method  has  the  advantage  that  the 
water  comes  in  contact  with  steam  and  is  heated  before  it 
mingles  with  the  water  in  the  boiler.  There  is  the  disadvan- 
tage  that  the  steam-pressure  may  Tall  off  when  the  feed-water 
is  turned  on  or  is  increased. 

It  has  already  been  pointed  out  that  the  feed-pipe  should 
have  a  globe  valve  near  the  boiler,  and  a  check-valve  between 
the  globe  valve  and  tne  feed-pump. 

Feed-pumps.  —  Boilers  are  commonly  fed  by  a  small  direct- 
acting  steam-pump  placed  in  the  boiler-room.  The  steam- 
consumption  per  horse-power  per  hour  of  such  pumps  is  very 
large,  and  yet  the  total  steam  used  is  insignificant.  They  are 
cheap  and  effective,  and  easily  regulated. 

If  the  boiler-pressure  is  over  100  pounds  an  outside  packed 
plunger  is  preferable  to  a  piston-pump. 

The  pump  should  be  of  the  duplex  type  and  the  plungers  at 
the  water  end  should  be  covered  with  a  composition  or  brass 
sleeve. 

Power  pumps  driven  from  a  large  engine  are  more  econom- 


BOILER    ACCESSORIES.  285 

ical,  provided  their  speed  can  be  regulated;  they  not  infre- 
quently arc  arranged  to  pump  a  larger  quantity  than  required 
for  feeding  the  boiler,  the  excess  being  allowed  to  flow  back  to 
the  suction  side  of  the  pump  through  a  relief-valve. 

When  one  pump  supplies  several  boilers,  a  series  of  diffi- 
culties is  liable  to  arise.  First,  if  the  boilers  are  fed  singly 
in  rotation,  the  large  intermittent  supply  of  feed-water  is 
likely  to  give  rise  to  local  contraction  and  the  water-level  in 
the  boiler  fluctuates;  there  is  liability  that  the  water-level  will 
fall  too  low,  endangering  the  heating-surface,  or  there  may  be 
excessive  priming  when  the  water-level  is  high.  It  appears 
advisable  that  the  feed  should  be  delivered  to  all  the  boilers 
simultaneously,  the  supply  to  each  boiler  being  regulated  by 
its  stop-valve;  each  branch  pipe  to  a  particular  boiler  should 
be  provided  with  its  own  check-valve,  and  the  water-level  and 
rate  of  feeding  of  each  boiler  must  be  carefully  watched  by 
the  fireman,  or  by  a  water-tender  if  there  are  many  boilers. 

Injectors. — An  injector  is  conveniently  used  for  feeding  a 
boiler  if  the  feed-water  is  not  too  hot;  it  has  the  incidental  advan- 
tage that  it  heats  the  water  as  it  feeds  it  into  the  boiler.  An 
injector  should  be  connected  up  with  unions,  so  that  it  may 
readily  be  taken  down  for  inspection.  At  sea  an  injector  is  com- 
monly used  when  the  boilers  are  fed  from  the  sea  or  from  a  supply- 
tank. 

Every  boiler  should  have  two  independent  sources  of  supply 
of  feed-water,  so  that  there  may  be  some  resource  if  the  usual 
supply  gives  out.  There  may  be  two  pumps,  or  a  pump  and  an 
injector.     A  locomotive  usually  has  two  injectors. 

As  the  amount  of  water  delivered  by  an  injector  can  be  varied 
only  by  a  small  amount,  and  as  an  injector  has  to  be  large  enough 
to  supply  a  boiler  at  the  time  of  maximum  demand,  it  follows 
that  under  the  ordinary  working  conditions  of  the  boiler  the 
injector  must  be  used  intermittently. 

Fig.   127   illustrates  a  Koerting  injector.     This  injector  has 


286 


STEAM-BOILERS. 


two  sets  of  tubes;    the  lower  or  lifting-tube  and  the  upper  or 
forcing-tube. 

After  opening  the  steam-valve  in  the  pipe  S  the  injector  is 
started  by  pulling  the  handle  about  il-  inches  to  the  left.  This 
uncovers  the  lower  steam-nozzle  or  lifting-nozzle. 


Fig.  127. 


As  soon  as  water  appears  at  the  overflow  O,  the  handle  is 
pulled  back  as  far  as  it  will  go.  This,  after  opening  the  lower 
steam-nozzle  wide  open,  opens  the  upper  steam-nozzle,  and  at  the 
same  time  pushes  down  the  overflow-valve  through  a  link  running 
along  the  side  of  the  injector.  It  will  be  noticed  that  the  water 
must  meet  with  considerable  resistance  in  passing  through  the 
various  passages  in  the  injector. 

Blow-off  Pipe. — The  blow-off  pipe  draws  from  the  lowest 
part  of  the  boiler,  or  from  some  place  where  sediment  may  be 
expected  to  collect.  On  the  blow-off  pipe  there  is  a  cock  or 
a  valve  which  is  opened  to  blow  out  water  from  the  boiler. 
Sometimes  there  are  both  a  cock  and  a  valve.  A  cock  has 
the  disadvantage  that  it  may  give  trouble  by  sticking;  a  valve 
may  leak  and  the  leak  may  not  be  detected. 


BOILER   ACCESSORIES. 


287 


The  pipe  should  be  carried  beyond  the  cock,  so  that  the 
attendant  is  not  liable  to  be  splashed  with  hot  water,  but  the 
pipe  should  end  in  the  boiler-room  or  where  discharge  through 
the  pipe  on  account  of  a  leaky  cock  or  valve  may  be  sure  to 
attract  attention.  Each  individual  boiler  should  have  its  own 
blow-off  pipe. 

The  blow-off  pipe  where  it  passes  through  the  back  con- 
nection is  covered  with  magnesia,  asbestos,  or  fire-brick.  In 
spite  of  this  protection  the  blow-off  pipe  may  burn  off.  The 
device  shown  by  Fig.  128  is  used  to  overcome  this  difficulty. 


Fig.  12S. 


When  the  blow-off  cock  is  shut  and  the  valve  on  the  vertical 
branch  is  open,  there  is  a  continuous  circulation  of  water 
which  keeps  the  pipe  from  burning.  The  vaive  on  the  verti- 
cal branch  is  closed  before  the  blow-off  cock  is  opened. 

If  a  blow-off  pipe  burns  off  and  water  begins  to  escape,  the 
feed-pump  should  be  run  at  full  capacity  to  keep  water  in  the 
boiler  and  guard- the  plates  from  burning,  if  that  is  possible. 
The  fire  should  then  be  checked  by  throwing  on  wet  ashes  or 
by  other  means,  unless  escape  of  steam  from  the  break  in  the 
blow-off  pipe  prevents. 


288  STEAM-BOILERS. 

Piping  to  carry  steam  from  a  boiler  to  an  engine,  for 
heating  buildings,  and  for  other  purposes  is  too  important  to 
be  considered  as  accessory  to  the  boiler.  A  iew  remarks,  how- 
ever, may  not  be  out  of  place. 

The  coefficient  of  expansion  of  steel  pipe  is  .0000065.  This 
means  that  for  each  degree  increase  in  temperature  the  pipe 
expands  this  fraction  of  its  length. 

Thus  a  pipe  at  700  F.  measures  100  feet.  What  will  be  the 
expansion  of  this  pipe  if  used  to  carry  superheated  steam  at  165 
pounds  absolute  pressure  with  1500  superheat? 

At  165  pounds  absolute  the  temperature  is  found  from  the 


u'balanced  expansion  joint 


Fig.  129. 


tables  to  be  365°.o.  F.;   add  150  to  this,  giving  5i5°.o.  as  the  tem- 
perature of  the  steam.     The  increase  of  temperature  is  515.9  —  70 


or  445°.o. 


445°.9X. 0000065  Xioo'Xi2"=i 


the  expansion  in  the  100  feet. 

In  a  long  line  of  high-pressure  piping  where  the  expansion  is 
6  or  more  inches,  the  expansion  may  be  taken  up  in  an  expansion- 
joint  like  that  shown  by  Fig.  129.  The  flanges  at  either  end  are 
connected  to  the  pipe. 


BOILER    ACCESSORIES. 


289 


The  drawing  needs  no  explanation. 

An  expansion-joint,  like  Fig.  129,  is  in  use  on  a  20-inch  pipe 
at  the  Merrimack  Mills  at  Lowell,  Mass.  The  following  figures 
on  expansion  were  obtained  by  the  chief  engineer: 

Length  of  20-inch  and  16-inch  pipe,  277  feet  8  inches. 
Temperature  of  outside  air,  560  F. 
Expansion  of  the  pipe  at  50  pounds  gauge,  45 1  inches. 
At  100  pounds  gauge,  5||  inches.     At  150  pounds  gauge, 
6]l  inches. 

In  long  runs  of  pipe  not  over  6  inches  in  diameter,  the  expan- 
sion may  be  allowed  for  by  screwed  fittings,  as  shown  by  Fig.  130. 


Fig.  130. 

The  pipes  shown  broken  are  anchored  at  either  end.  The 
length  of  the  pieces  running  at  right  angles  depends  upon  the 
amount  of  expansion  to  be  taken  care  of. 

As  arranged  there  is  no  chance  to  pocket  water  in  the  expan- 
sion-joint. A  drip  should  be  provided  at  the  end  of  the  pipe 
bringing  steam  into  the  joint. 

A  common  way  of  allowing  for  expansion  is  l'lustrated  by 
Fig.  131,  which  shows  the  connection  from  a  boiler  to  the  main 
steam-pipe.  When  the  main  steam-pipe  expands  or  contracts, 
the  short  nipple  between  it  and  the  angle-valve  tu*ns  a  little  at 
one  or  at  both  ends;  in  like  manner  the  vertical  pipe  turns  a 
little  at  the  nozzle  or  at  the  elbow.  The  motion  is  so  small  and 
so  distributed  as  not  to  give  any  trouble  unless  thf  expansion  to 
be  provided  for  is  very  large. 


290 


STEAM-BOILERS. 


Fig.  T31  is  so  arranged  that  there  is  no  space  where  water 
can  collect  when  the  boiler  is  shut  off  from  the  main  steam- 
pipe.  If  the  stop-valve  were  in  the  vertical  pipe,  as  is  some- 
times the  case,  then  the  pipe  over  the  valve  would  fill  up  with 
water   when  the   boiler   is   shut  off,    and   that  water  would   be 


Fig.  I31- 


suddenly  blown  into  the  steam-main  when  the  stop-vaive  is 
next  opened.  A  pipe  so  situated  should  always  have  a  drip- 
pipe  to  draw  off  condensed  water  before  the  valve  is  opened. 
As  a  special  example  we  may  mention  the  pipe  leading  to  an 
engine,  which  always  has  a  drip-pipe  above  the  throttle-valve. 
Pipes  that  are  likely  to  be  troubled  by  condensation  should 
be  continuously  drained  by  a  steam-trap. 

Horizontal  pipes  are  sometimes  arranged  so  that  water  may 
collect  in  them,  due  to  a  sag  in  the  pipe  or  to  the  fact  that 
they  do  not  properly  drain  through  a  side  branch.  Though 
the  water  may  lie  quiet  in  such  a  pocket  while  the  draught  of 
steam  is  steady,  a  sudden  increase  in  the  velocity  of  the  steam, 
or  a  rapid  opening  of  the  valve  supplying  steam  to  the  pipe, 
will  sweep  the  water  up  and  carry  it  along  with  the  steam.  The 
danger  from  the  inrush  of  water  to  an  engine  is  readily  seen, 
but  it  is  not  so  well  known  that  the  water  thus  violently  thrown 


BOlLhR   ACCESSORIES.  2oi 

against  elbows  and  other  fittings  give  rise  to  leaks,  if  it  does  not 
burst  the  fittings.  It  is  to  be  remembered  that  steam  offers 
little  or  no  resistance  to  the  movement  of  water  in  a  pipe,  as  it 
is  readily  condensed  either  from  a  slight  increase  of  pressure 
or  by  mingling  with  colder  water.  Again,  water  at  the  temper- 
ature corresponding  with  the  pressure  easily  separates,  forming 
bubbles  of  steam,  which  as  easily  collapse,  and  the  shock  of 
impact  of  the  water  gives  rise  to  pressures  that  search  out 
all  weak  places  in  the  pipe,  even  at  some  distance. 

Steam-piping  should  be  pitched  in  the  direction  of  the  flow 
of  the  steam  sufficiently  to  drain  out  the  condensation. 

Should  a  large  pipe  be  connected  to  one  of  smaller  diameter, 
the  bottom  of  the  inside  of  the  pipes  must  be  kept  on  the  same 
level.  For  this  purpose  eccentric  flanges  and  tees  with  eccentric 
outlets  may  be  used. 

To-day  nearly  all  of  the  high-pressure  piping  is  put  up  with 
elbows  made  of  bent  pipe  instead  of  cast-iron  or  gun-iron  flanged 
fittings.  The  bent  pipe,  by  giving,  allows  for  expansion,  and  it 
also  reduces  the  friction  loss  in  passing  through  the  quarter  turn. 
The  radius  of  the  bends  is  commonly  made  equal  to  five  diam- 
eters of  the  pipe. 

To  get  some  idea  as  to  the  stiffness  of  these  bent  pipes  the 
following  tests  on  bent  pipes  were  made  at  the  Massachusetts 
Institute  of  Technology  by  two  seniors  under  the  direction  of  one 
of  the  writers: 

The  figures  marked  Pipes  Nos.  1-9  give  the  size  and  weights. 
The  load  was  applied  at  the  points  marked  by  the  arrows,  and 
deflections  were  measured  at  points  indicated  by  the  dash  and 
dot  lines. 

Fig.  132  illustrates  the  best  practice  in  connecting  a  boiler  to 
the  main.  The  pipe  is  given  a  slight  pitch  towards  the  main. 
There  are  two  straight-way  valves  with  advancing  stems  and  a 
blanked  tee  in  the  line.  The  three  may  be  bolted  together. 
The  valve  operated  by  the  chain  has  a  by-pass  (not  shown). 

If  a  boiler  is  piped  to  the  main  in  this  way  there  is  no  danger 


2p2 


STEAM-BOILERS. 


$2f 


^ 


Weight  =  552  1bs.    Outfidedia.tt.625      Inside  dia.  C.065 


Weight  =133  lbs.    Outside  dia.3.500,   Inside  din.  3.067 


6*9* 


s->m,-ii-,- 


_L_ 


BOILER    ACCESSORIES. 


2  93 


PLTE  No.  i. 
Outer  dia.  5".     Inner  dia.  4.25". 


PIPE  No.  2. 

Outer  dia.  6.625".     Inner  dia.  6.065". 


Total  Motion  in  Inches. 

Load, 

At  Outer 

At  Inner 

Line. 

Line. 

200 

.060 

.025 

400 

125 

.050 

600 

185 

.076 

800 

250 

io5 

IOOO 

3ii 

*33 

I200 

372 

.160 

I4OO 

435 

.185 

160O 

499 

.213 

l800 

.S61 

.240 

2000 

625 

.265 

Total  Motion  in  1  riches 

Load, 

Pounds. 

At  Outer 

At   Middle 

At  Inner 

Line. 

Line. 

Line 

600 

-29 

.16 

.08 

I200 

•58 

-31 

.16 

1800 

-87 

■45 

23 

24OO 

I. 16 

.61 

3> 

3000 

I  .  so 

.78 

•39 

3600 

1.88 

; 

.96 

.4<S 

PIPE  No.  3. 
Outer  dia.  6.625".     Inner  dia.  6.065". 


Total  Motion  in  Inches 

. 

Load. 
Pounds. 

At  (  hiter 

At  Second 

At  Third 

At  Inner 

Line. 

Line. 

Line. 

Line. 

200 

1 .  20 

O.83 

0.  50 

0.  17 

400 

2-35 

I.65 

o.g7 

0-34 

600 

3-55 

2.45 

1-45 

0.80 

800 

4.70 

3-3° 

i-95 

0.67 

IOOO 

5-9° 

4.i5 

2-55 

O.86 

1200 

7-30 

5.  20 

3.20 

1    10 

1400 

9-i5 

6.50 

4.00 

1    5° 

PIPE  No    4. 
Out.  dia.  6.625".   In.  dia.  6.025' 


Total  Motion 

in  Inches 

Load, 

Pounds. 

At  <  )uter  i  At  Inner 

Line.             Line. 

IOOO 

.050            .015 

2000 

.107             .030 

3000 

.167             .045 

4000 

. 230            . 060 

SOOO 

-293 

.080 

6000 

•365 

.  100 

7000 

-442 

.123 

8000 

.542 

.155 

8500 

.603 

.174 

PIPE  No.  5 
Outer  dia.  5.563."     Inner  dia.  5.045". 


Load, 
Pounds. 

Total  Motion  in  Inches. 

At  Outer          At  Inner 
Line.                 Line. 

IOOO 

2000 

3000 

3500 

-205                 .058 
.407                 .115 
.612                 .177 
.740                 .216 

294 


STEAM-BOILERS. 


PIPE  No.  6. 
Outer  dia.  8.62".      Inner  dia.  7.62". 


PIPE  No.   7. 
Out.  dia.  7.625".     In.  dia.  7  023" 


Total  Motion  in  Inches. 

Load , 
Pounds. 

At  Outer 

At  Middle 

At  Inner 

Line. 

Line. 

Line. 

1000 

•175 

.108 

.050 

2000 

•345 

217 

.  IOO 

3000 

.516 

•324 

.151 

4000 

•695 

-435 

.205 

5COO 

.860 

•542 

.255 

6000 

1.032 

.652 

•307 

/OOO 

1   206 

.761 

.360 

8000 

1  375 

.872 

.410 

8500 

1.463 

.932 

.440 

PIPE  No.  8. 
Out.  dia.  3.500  '.     In.  dia.  3.067". 


Load. 
Pound*. 

Total  Motion  in  Inches. 

At  Outer 
Line. 

At  Middle 
Line. 

At  Inner 
Line. 

IOO 
200 
300 
400 

.820 
1.620 
2.420 
3.280 

.441 

.880 

I.320 

1. 912 

.124 
.248 
.380 
.560 

Total  Motion 

in  Inches. 

Load . 
Pounds. 

At  Outer 

At  liner 

Line. 

Line. 

1000 

.182 

.080 

2000 

S9Q 

.160 

3000 

.628 

.  252 

4000 

.892 

.366 

5000 

1.225 

.510 

5500 

1.480 

.618 

PIPE  No.  9. 
Out.  dia.  3.500".     In.  dia.  3.067' 


Total  Motion  in  Inches. 

Load, 
Pounds. 

At  Outer 
Line. 

At  Inner 
Line. 

200 

.158 

•037 

400 
600 
800 

-311 
.466 
.620 

.071 
.  106 
- 142 

IOOO 
1200 

•775 
•  95° 

.178 
.228 

1400 

1. 215 

319 

M, 


Fig.  132. 

in  going  inside  the  boiler  even  though  there  may  be  200  pounds 
pressure  in  the  main.     By  shutting  both  valves  and  uncovering 


BOILRP     ACCESSORIES. 


2<)$ 


the  outlet  on  the  blanked  tee  there  is  no  possibility  of  steam 
leaking  back  into  the  boiler. 

The  outlet  of  the  tee  may  be  on  the  side  or  on  the  bottom. 
Piping  must  be  anchored  at  some  point.  Generally  there 
must  be  an  anchorage  near  the  engine.  Each  system  of  piping 
has  to  be  considered  by  itself,  and  no  general  rule  can  be  given. 
A  simple  form  of  anchor  is  shown  by  Fig.  133.  If  a  pipe 
passes  through  a  brick  wall  a  clamp  may  be  made  to  fasten  to  the 
pipe  and  to  bear  against  the  wall. 

Fig.  134  shows  a  method  used  in  supporting  large  pipes.  The 
top  roller  is  generally  omitted. 

Small  piping,  up  to  8  or  10  inches,  is  frequently  hung  by 
rings. 

Figs.  135,  136,  and  137  show  three  of  the  forms  of  flanged 
joint  used  on  high-pressure  piping.  Fig.  137  is  known  as  the 
Van  Stone  joint. 

Bursting  Pressure  of  Extra  Heavy  Flanged  Fittings. — 
— An  investigation  as  to  the  strength  of  fittings  was  made  by  the 
Crane  Company  and  the  results  of  their  tests  published  in  The 
Valve  World  of  Nov.,  1907.  From  their  tests  they  deduced  the 
following  formula: 

T  =  thickness  of  metal; 
D  =  inside  diameter; 
B  =  bursting  point; 

5  =  65  per  cent  of  tensile  strength  of  the  metal  up  to  12 
inches  diameter  and  60  per  cent  for  sizes  over  12 
inches  diameter. 


T 


For  working  pressure  divide  B  by  a  factor  of  from  4  to  8  as  desired. 
Vibration  of  Steam-pipes. — Steam  pipes-connected  to  high- 
speed  engines   seldom   vibrate    much.     Pipes   leading   to   slow- 
speed  engines  often  vibrate  badly. 


296 


STEAM-BOILERS. 


Fig.  133. 


Fig.  134. 


Fig.  135. 


Fig.  136. 


Fig.  137. 


BOILER    ACCESSORIES. 


2<>7 


An  engine,  rigid  on  its  foundation,  may  set  up  vibrations  in  a 
pipe  through  pulsations  caused  by  the  checking  of  the  velocity  of 
the  steam  at  cut-off.  Such  vibrations  are  most  apt  to  oocur  in 
pipes  which  are  amply  large  for  the  engine. 

In  most  cases  of  vibration,  if  the  stop-valve  on  the  boiler  is 
closed  so  as  to  make  a  slight  drop  in  pressure  at  the  engine,  2 
or  3  pounds,  the  vibration  will  cease.  A  large  drum  placed  close 
to  the  engine  with  a  throttling-valve  in  the  steam-pipe  entering 
the  drum  will  accomplish  the  same  result.  The  valve  close  to 
the  drum  will  then  be  used  to  stop  the  vibration 

Area  of  Steam-pipe. — In  order  that  the  loss  of  pressure 
in  a  steam-pipe  due  to  friction  may  not  be  excessive,  it  is 
customary  to  limit  the  velocity  to  5000  or  6000  feet  per  min- 
ute. If  there  are  many  bends  or  elbows  in  the  pipe,  the 
velocity  may  be  4800  feet  per  minute,  or  less. 

Example. — Required  the  diameter  of  the  main  steam-pipe 
leading  from  a  battery  of  boilers  having  an  aggregate  of  3000 
boiler  horse-power.  Assume  the  pressure  to  be  100  pounds 
by  the  gauge,  or  about  115  pounds  absolute.  Assume  also 
that  a  boiler  horse-power  is  equivalent  to  30  pounds  of  steam 
per  hour.  Then  the  steam  drawn  from  the  boiler  in  one  hour 
is 

30  X  3000  =  90,000 

pounds.     The  steam  per  minute  is  consequently  1 500  pounds. 
Now  one  pound  of  steam  at  115   pounds   absolute  has   a 
volume  of  3.88  cubic  feet.     Consequently 

1500  X  ^.8S  =  5820 

cubic  feet  of  steam  per  minute  must  pass  through  the  steam- 
main.  With  a  velocity  of  5000  feet  per  minute  the  area  o 
the  pipe  must  be 

5820  -f-  5000  =  1. 164 


2q8  steam-boilers. 

square  feet,  or  167.6  square  inches.  The  corresponding  diameter 
is  14!  inches.  The  next  larger  size  of  pipe  is  16  inches,  which 
will  be  used. 

In  calculating  the  size  of  the  steam-pipe  needed  for  a  battery 
of  boilers  the  lowest  pressure  at  which  the  boilers  will  ever  work 
must  be  considered,  for  a  pipe  which  will  carry  500  H.P.  at  150 
pounds  pressure  will  carry  only  about  3/4  of  500  at  100  pounds 
pressure  with  the  same  velocity. 

Flow  of  Steam  in  Pipes. — Various  formulae  have  been 
proposed  for  use  in  figuring  the  weight  of  steam  a  pipe  will  deliver 
with  a  cretain  drop  in  pressure. 

An  article  by  Prof.  G.  F.  Gebhardt  in  Power,  1907,  compares 
all  of  these  formula?. 

It  would   seem  that   the  formulae  proposed  by  Mr.   G.  H. 
Babcock  give  results  which  agree  very  closely  with  results  ob- 
tained by  experiment. 
In  this  formula 

iv  =  the  weight  of  steam  in  pounds  per  minute; 
d= diameter  of  pipe  in  inches; 
L  =  length  of  pipe  in  feet; 

P  =  the  drop  in  pressure  in  pounds  per  square  inch; 
y  =  the  mean  density  in  pounds  per  cubic  foot; 
V=  velocity  in  feet  per  minute. 


^  =  15,950 


Pd 


H+t)' 


w=Sj 


Pyd5 


w2L[  ] 
P==  .0001321 


BOILER    ACCESSORIES. 


299 


Pipe-covering'. — The  steam-pipes  should  be  covered  with 
some  non-conducting  material  to  prevent  radiation  of  heat. 
Magnesia,  asbestos,  mineral  wool,  hair-felt,  etc.,  have  been  used 
for  such  coverings. 

Generally  a  sectional  covering  is  used  on  the  straight  pipe  and 
plastic  on  the  fittings. 

It  is  probable  that  four  tenths  of  a  heat-unit  will  be  lost  per 
square  foot  of  pipe  surface  per  hour  per  degree  difference  of 
temperature  between  the  steam  inside  the  pipe  and  the  air,  if  any 
good  covering  from  1  inch  to  i\  inches  in  thickness  is  used.  A 
bare  pipe  would  lose  from  2.5  to  3  heat-units  in  radiation  from 
each  square  foot  per  hour  and  per  degree  difference  of  temperature. 
The  saving  to  be  made  by  covering  the  pipes  is  apparent. 

Tube-cleaners. — To  remove  the  scale  which  collects  on  the 
inside  of  the  tubes  of  water-tube  boilers  supplied  with  a  poor 
grade  of  feed-water,  turbine  tube-cleaners  are  used. 

Figs.  138  and  139  show  the  Liberty  tube-cleaners.     The  head, 


Fig.  138. 


shown  by  Fig.  138,  is  for  hard  scale,  and  also  for  use  in  a  bent 
tube. 

Fig.  139  shows  a  different  head  attached  to  the  turbine.  The 
turbine  blades  are  seen  in  Fig.  139.  Water  from  a  hose  is  taken 
into  the  outer  casing.  The  water  in  escaping  passes  through 
the  turbine,  which  rotates  at  high  velocity,  throwing  the  arms 
with  cutters  out  by  centrifugal  force.  The  scale  removed  is 
washed  away  by  the  water. 

The  Weinland  turbine  cleaner  is  shown  by  Figs.  140  and  141. 


3°° 


S1EAM-B0ILERS. 


Fig.  139. 


Fig.  140. 


Fig.  141. 


^^fefe;.- 


Fig.  142. 


BOILER     ACCESSORIES. 


301 


The  lower  right-hand  figure  is  in  section.  The  porcupine  head 
which  is  used  on  heavy  scale,  is  shown  at  the  left. 

This,  like  the  preceding,  operates  with  a  H-inch  hose. 

A  cleaner  for  removing  soot  from  the  inside  of  fire-tubes  is 
shown  by  Fig.  142.  This  is  attached  to  a  long  rod  and  pushed 
through  the  tube. 

Coal  Conveyers. — Two  types  of  coal-conveyers  are  used 
for  elevating  coal  from  the  ground  to  the  hoppers  supplying  the 
boilers  or  to  the  coal-pocket;  the  iron  bucket  conveyer  and  the 
belt-conveyer.     Fig.  143  shows  a  bucket-conveyer  and  the  method 


Fig.  143. 

of  driving  it.  The  buckets  are  joined  together  by  an  endless 
chain  made  of  links  supported  by  flanged  wheels  on  a  track.  The 
buckets  are  free  to  swing  about  their  point  of  attachment  to 
the  links. 

The  driving-gear  carries  a  number  of  pawls  which  are  so 
guided  at  their  inner  ends  by  a  fixed  cam  that  each  in  succession 
pushes  on  pins  or  studs  projecting  from  the  link-chain. 

The  conveying-buckets  swing  freely  on  pivots,  so  thU  it  is 
necessary  to  load  them  evenly  to  prevent  tipping.  This  loading 
is  accomplished  by  the  filler,  Fig.  144.  It  has  a  series  of  bottom- 
less shells  which  fit  the  buckets  of  the  conveyer.  It  also  prevents 
coal  from  dropping  between  the  buckets  as  they  are  filled.  The 
filler  is  driven  by  the  conveyer,. 


3o: 


STEAM-BOILERS. 


A  set  of  rolls,  such  as  is  used  for  supporting  a  24-inch  belt  on 
a  belt-conveyer,  is  shown  by  Fig.  145.     Sets  of  rolls  are  placed 


close  together. 


Fig.  144. 
The  end  rolls  of  each  set  are  inclined  so  that  the  carrying  side 


of  the  belt  is  bent  into  an  arc  of  a  circle, 
elevated  at  an  angle  of  1 70  without  rolling. 


Soft  coal  has  been 


^^ 


Fig.  146. 

A  distributing  tripper  is  shown  by  Fig.  146. 
The  conveying  belt  brings  the  material  from  the  left  as  shown 
in  the  cut  and  passes  over  roller  B  and  then  over  C  and  passes 


BOILER    ACCESSORIES.  303 

along  to  the  right.  As  the  belt  goes  over  B  the  material  on  it  is 
dumped  through  the  chute  of  the  tripper.  The  tripper  is  sel 
on  a  truck  (D)  which  moves  on  a  track.  It  is  moved  by  means 
of  a  clutch,  regulated  by  handle  A,  which  puts  the  gear  E  into 
connection  with  B  or  C,  which  are  revolving  in  opposite  direc- 
tions. The  tripper  may  be  set  so  as  to  discharge  over  any  space 
desired.  The  handle  A,  by  striking  against  dogs  placed  at  either 
end  of  the  travel  of  the  carriage,  automatically  shifts  the  clutch 
driving  the  gear  E  and  causes  reversal. 


CHAPTER   X. 
SHOP-PRACTICE. 

THE  method  of  work  in  a  boiler-shop  depends  on  the  size 
and  arrangement  of  the  shop  and  on  the  class  of  work. 
There  are,  however,  certain  general  principles  which  can  be 
recognized  in  all  modern  shops. 

The  materials,  especially  the  plates,  are  received  at  one 
end  of  the  shop,  near  which  is  a  storeroom,  and  a  bench  for 
laying  out  work.  The  plates,  after  they  are  laid  out,  pass  in 
succession  to  the  several  machines,  where  they  are  sheared, 
punched  or  drilled,  planed,  rolled,  and  riveted.  The  machines 
for  performing  these  operations  are  arranged  in  order  with 
proper  spaces  for  handling  and  working.  Space  is  provided 
where  boilers  may  be  assembled  and  receive  their  tubes  and 
furnaces.  Machines  which,  like  the  punch,  have  much  work- 
to  do,  compared  with  other  machines,  may  be  duplicated. 

There  should  be  an  efficient  system  for  handling  the 
material  at  the  machines  and  for  passing  it  on  from  one 
machine  to  the  next.  A  good  arrangement  is  to  have  a 
swing-crane  near  each  machine ;  the  spaces  served  by  the 
several  cranes  overlap,  so  that  one  crane  takes  material  from  the 
next,  and  so  on.  It  is  advantageous,  especially  in  large  shops, 
to  have  a  travelling  crane  that  can  handle  the  largest  boiler 
made,  and  which  can  serve  any  part  of  the  shop. 

Flanging  and  smithing  are  usually  done  in  a  separate  shop 
or  room.  A  few  machine-tools  are  needed  for  doing  work  on 
steam-nozzles,  manhole  rings  and  covers,  etc. 

A  boiler-shop  will  have  an  office,  a  drawing-room,  and  a 

304 


SHOP-PR  A  CTICE.  305 

pattern-room,  also  a  storeroom  for  patterns.     These  may  be 
conveniently  located  in  the  second  story. 

A  Boiler-shop. — The  application  of  the  general  princi- 
ples just  stated  and  the  explanation  of  details  can  be  best 
given  by  aid  of  an  example.  A  medium-size  shop  for  making 
cylindrical  boilers  has  been  chosen  for  this  purpose;  the 
shop  is  capable  of  making  any  shell  boiler  of  moderate  size. 
This  shop  will  employ  sixty  or  seventy  men  and  can  turn  out 
two  100-horse-power  boilers  per  day.  It  will  take  about 
three  days  to  finish  one  boiler,  so  that  there  may  be  six  or 
more  boilers  in  process  of  construction  at  one  time. 

The  shop  which  is  represented  by  Fig.  147  has  one  end 
on  the  street  and  has  a  driveway  or  yard  at  one  side.  Plates 
are  received  at  the  street-door  by  a  travelling  crane  and  stored 
near  at  hand.  The  same  crane  takes  plates  to  the  laying-out 
bench  and  from  there  to  the  crane  which  serves  the  shearing- 
machine.  Along  one  side  of  the  shop  are  arranged  in  suc- 
cession a  shearing-machine,  two  punches,  a  plate-planer,  a 
set  of  plate-rolls,  and  a  riveting-machine.  Between  the 
punches  and  nearer  the  wall  is  a  flange-punch ;  near  the 
planer  is  a  forge  for  scarfing.  This  series  of  machines  is 
served  by  four  swing-cranes,  and  there  are  also  two  hydraulic 
cranes  near  the  riveting-machine.  These  cranes,  which  are  at 
the  top  of  a  tower  thirty  feet  high,  are  operated  from  the 
working  platform  of  the  riveter.  There  are  two  shipping- 
doors  where  the  finished  boiiers  are  delivered  to  teams,  and  at 
each  door  there  is  a  jib-crane  for  handling  the  boilers.  These 
jib-cranes  and  the  hydraulic  cranes  at  the  riveter  have  a 
capacity  of  eight  or  ten  tons ;  the  swing-cranes  may  be  much 
lighter.  A  shop  where  large  marine  boilers  are  made  will 
have  more  powerful  cranes. 

The  machine-shop  is  near  the  receiving-door.  Here  are 
the  lathes,  planers,  and  drills  for  doing  work  on  manholes, 
nozzles,  and  other  fittings  ;  also  a  bench  for  fitting  up  boiler- 
fronts.      Two  drills  for  boring  tube-holes  in  tube-plates,  and 


3°6 


S  TEA  M-BOILERS. 


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SHOP-PR  A  CTICE. 


307 


a  boring-mill  for  facing  off  the  flanges  of  boiler  heads,  are 
placed  in  the  entrance  to  the  machine-shop,  where  work  can 
be  conveniently  brought  to  them  from  the  boiler-shop.  At 
the  end  partition  of  the  machine-shop  are  places  for  storing 
boiler-front  castings  and  sheet-iron.  The  corner  of  the  boiler- 
shop  near  the  machine-shop  is  known  as  the  cold-iron  shop ; 
here  the  uptakes,  flues,  and  dampers  are  made.  This  shop 
has  a  shearing-machine,  three  punches,  and  a  set  of  rolls 
suitable  for  sheet-iron  work;  also  a  bench  with  hand-vises. 

At  the  rear  of  the  boiler-shop  there  is  in  one  corner  a  store- 
room for  tubes,  stay-rods,  channel-bars,  and  finished  fittings. 
In  the  opposite  corner  are  the  forge-shop  and  the  engine- 
room.  These  are  separated  from  each  other  and  from  the 
boiler-shop  by  glass  partitions  which  do  not  cut  off  the  light, 
and  yet  keep  the  smoke  and  dust  from  the  forge  out  of  the 
other  rooms. 

The  main  line  of  shafting  is  near  the  wall  over  the  shear- 
ing-machine, punches,  and  rolls.  The  shafting  for  the  ma- 
chine-shop and  cold-iron  shop  is  driven  by  a  belt  from  the 
main  shaft,  near  the  front  end  of  the  building.  A  space  is 
left  near  the  riveter  where  the  plates  from  the  rolls  can  be 
assembled  and  bolted  together  before  going  to  the  riveter. 
In  front  of  the  riveter  there  is  a  space  about  60  feet  wide 
and  120  feet  long  where  boilers  are  deposited  after  leaving 
the  riveter.  Here  the  boilers  receive  their  stays  and  tubes, 
here  they  are  calked  and  receive  all  fixtures  that  are  perma- 
nently attached  to  the  shell.  At  this  place  the  boilers  are 
tested  by  hydraulic  pressure,  usually  to  one  and  a  half  times 
the  working  pressure.  When  complete  the  boilers  are  painted 
and  oiled,  ready  for  shipment. 

To  illustrate  the  method  of  building  a  boiler  more  in 
detail,  the  different  steps  in  making  a  horizontal  boiler  will 
be  followed  in  order. 

Flanging  Heads. — Regular  sizes  of  boiler-heads  flanged 
at  one  operation  by  machinery  can   now   be    bought    on   the 


308  STEAM-BOILERS. 

market,  and  all  except  the  largest  shops  are  in  the  habit  of 
buying  them.  The  flanging-machine  has  a  former  and  a  die 
between  which  the  plate  is  formed  under  hydraulic  pressure 
while  at  the  proper  flanging  temperature.  No  strains  due  to 
unequal  heating  or  cooling  are  set  up  in  this  process,  and 
the  plate,  which  is  allowed  to  cool  gradually,  does  not  need 
to  be  annealed. 

Irregular  sizes  and  shapes  are  made  in  the  shop  on  a 
special  cast-iron  anvil,  which  is  about  six  inches  deep,  flat  on 
top,  and  curved  at  one  side  to  about  the  radius  of  the  head  to 
be  flanged.  The  corner  of  the  anvil  or  former  is  rounded  so 
as  not  to  cut  the  plate.  It  is  placed  near  a  special  low  forge 
where  the  plate  is  heated. 

In  flanging,  the  plate  is  first  marked  at  short  distances  on 
the  inner  circle  of  the  bend  with  a  prick-punch.  A  portion 
of  the  plate  is  then  heated  to  a  good  heat,  and  the  plate  is 
taken  to  the  anvil  or  former.  After  adjusting  so  that  the 
depth  of  flange  overhangs  the  right  distance  from  the  edge 
of  the  former,  the  heated  portion  of  the  plate  is  beaten  down 


Fig.    148. — Lifting-dogs. 

against  the  side  of  the  former  by  wooden  mauls  and  then 
smoothed  with  a  flatter  and  sledge.  The  plate  is  then  heated 
in  a  new  place  and  another  portion  bent.  To  straighten  the 
head  and  also  to  remove  the  strains  set  up  by  this  way  of 
flanging,  it  should  be  heated  to  a  dull  red  and  allowed  to  cool 
gradually. 

The  lifting-dogs  represented  by  Fig.  148  are  used  in  lift- 


SHOP- PR  A  CT1CE. 


.?09 


ing  and  placing  the  head  during  the  flanging,  and  in  handling 
plates  during  other  operations. 

Fig.  149    represents  crane-lifts  which  are   used  when  plates 
are  lifted  and  carried  by  cranes. 


Fig.  149. 

After  the  head  is  flanged,  holes  for  rivets,  stay-rivets, 
and  tubes  are  marked,  and  all  the  rivet-holes  are  punched. 

Flange-punch. — The  holes  in  the  flange  are  punched  by 
a  special  machine  shown   by  Fig.  T50.       The  punch  is  carried 


Fig.  150. 

by  a  horizontal  wrought-iron  plunger  which  is  operated  by  a 
cam.  The  die  is  carried  by  a  hooked  extension  of  the  frame. 
The  head  is  held  horizontal  with  the  flange  down  ;  the  flange 
is  dropped  between   the  punch  and  the  die  and  the  lever  is 


3io 


S  TEA  M- BOILERS. 


solid   piece  of  tool-steel. 


Fig.  151. 


pulled  to  throw  the  cam  into  play ;  the  plunger  then  makes 
a  stroke  and  punches  a  hole.  The  machine  is  driven  by  a 
belt,  with  a  fast-and-loose  pulley.  On  the  shaft  with  these 
pulleys  is  a  heavy  fly-wheel.  A  pinion  and  spur-gear  give  a 
slow  powerful  stroke  to  the  gear  which  moves  the  cam. 

Punch  and  Holder. — The  punch  (Fig.  151)  is  made  of  a 

It  has  a  flat  head  and  a  conical 
shoulder  by  which  it  is  held  onto 
the  plunger,  a  short  straight  body, 
and  a  slightly  coned  point.  The 
point  is  larger  at  the  cutting  edge 
than  back  toward  the  straight 
body,  to  avoid  friction  in  the  hole. 
A  tit  in  the  middle  of  the  face  of 
the  punch  catches  in  the  centre- 
punch  mark  and  centres  the  hole  punched. 

The  holder  is  made  of  wrought  iron.      It  screws  onto  the 
end  of  the  plunger,  grips  the   punch  by  the  conical  shoulder 
on  its  head,  and  draws  it  down  firmly  against  the  plunger. 
Tube-holes. — There  are  two   ways  of  cutting  the  holes 
for    the    tubes   in    boiler-heads.      Some- 
times a  small  hole    is   punched    at    the 
centre   of   the   hole.     A  tool    like    that 
shown  by  Fig.    118  is  then  put  in  the 
drill-press.     The  post  in  the  middle  is 
run    through  the  small  hole  previously 
punched  or  drilled,  and  the  two  cutters 
rapidly   cut    out    the    tube-hole    to    the 
proper  size. 

The  other  way  is  to 
punch  the  tube-holes 
at  once  to  the  proper 
size  by  a  helical  punch 
shown  by  Fig.  1 19.  The  die  is  made  in  the  form  of  a  ring 
with   a  flat   face,   so  that  the  punch  begins  to  cut  at  the  cor- 


u 


Fig.  152. 


Fig.  153- 


SHOP-PR  A  CTICE. 


3" 


ners,  and  the  metal  is  removed  by  a  shearing  cut.  Though 
not  always  dune,  the  holes  ought  to  be  punched  a  little  under 
size  and  then  reamed  out  to  give  a  fair  surface  against  which 
the  tubes  may  be  expanded. 

Finishing  the  Flange. — The  boiler-heads  are  placed  on 
the  platen  of  a  boring-mill  like  that  shown  by  Fig.  154,  and 
the  edge  of  the  flange  is  turned  off.  The  heads  of  marine 
boilers  are  often  turned  to  a  true  cylinder  at  the  flange  to  insure 
that  they  shall  exactly  fit  the  cylindrical  shell  into  which 
they  are  riveted.  This  also  gives  a  good  surface  to  calk 
against. 

Boring-mill. — A  simpler  machine  than  the  boring-mill 
shown  by  Fig.  154  would  answer  to  turn  off  the  flanges  of 
the  boiler-heads.  But  the  machine  is  useful  in  other  ways 
and  may  do  the  work  which  is  commonly  done  on  a  large 
lathe. 

The  platen  is  driven  much  in  the  same  manner  as  the 
head  of  a  lathe,  through  gearing  and  cone  pulleys,  to  provide 
for  various  speeds.  This  gearing  is  not  well  shown  in  the 
figure,  as  it  is  hidden  by  the  frame.  The  cutting-tool  is  ad- 
justed and  controlled  much  like  the  tool  of  a  planer.  The 
tool-carriage  is  on  a  horizontal  cross-head  which  is  supported 
at  the  side  frame  and  on  a  round  vertical  bar  at  the  middle. 
The  tool  can  be  traversed  in  and  out  on  the  cross-head,  and 
the  cross-head  may  be  raised  or  lowered. 

For  doing  some  classes  of  work  the  cross-head  may  be 
set  vertically  on  the  guides  that  are  shown  on  the  horizontal 
bars  of  the  frame  near  the  right-hand  end.  Or,  again,  a  tool 
may  be  carried  by  the  central  rod.  which  can  be  fed  down  by 
the  screw  at  the  top. 

Laying  on  the  Plates.— The  first  and  one  of  the  most 
important  steps  in  the  work  on  the  shell  is  the  marking  out 
of  the  plates.  Generally  one  man  in  each  shop  does  all  the 
laying  out.  After  squaring  the  sheet,  he  marks  off  the 
length  and  locates  the  rivet-holes  by  means  of  gauges.      These* 


312 


S  TEA  M-BOILERS. 


gauges  have  to  be  made  by  trial,  a  suitable  allowance  being 
made  in  them  on  account  of  the  thickness  of  the  plate  for  the 


Fig.  154. 


change  in  length  due  to  rolling.     There  is  a  gauge  for  each 
course,  or  a  set  of  gauges  for  each  size   boiler,  and  also  sets 


SHOP-PA  A  CTICE. 


3*  3 


for  the  same  size,  but  with  different  thickness  of  shell.     The 
plates  are  marked  either  with  a  piece  of  soapstone  or  with  a 
slate-pencil.      Rivet-holes  are  prick-punched  at  the  centre. 
Shearing. — When  the  plate  is  laid   out  it  is  taken    from 


Fig.   155. 

the  bench  to  the  shears  and  any  superfluous  stock  is  cut  off. 
A  shearing-machine  is  shown  by  Fig.  155.  The  lower  knife 
is  fixed  and  the  upper  knife  is  moved  by  an  eccentric  inside 
the  head.  The  eccentric-shaft  is  coupled  to  the  gear-shaft 
by  a  clutch  that  is  controlled  by  a  treadle.  The  weight  of  the 
sliding-head  is  counterbalanced  by  a  weight  and  lever  at  the 
top.  Lugs  are  shown  on  the  casting  near  the  knives:  when 
the  machine  is  required  to  do  extra-heavy  work,  wrought-iron 
bolts  are  put  through  the  lugs  and  screwed  up  to  strengthen 
the  frame. 

The  machine  is  driven  by  a  belt  with  a  fast-and-loose  pul- 
ley; the  shaft  carrying  these  pulleys  has  a  pinion  gearing  into 
a  large  gear  to  give  the  necessary  power  for  shearing.  A  Ayr 
wheel  steadies  the  motion  of  the  machine;  it  must  be  able  to 
supply  the  power  for  shearing-plates  without  a  large  reduction 
in  speed. 


314  S  TEA  M-BOILERS. 

Punch.— After  the  plate  is  sheared  to  size  it  is  taken  to 
one  of  the  punches  and  all  the  rivet-holes  are  punched.  Larger 
openings  for  man-holes  and  other  fittings  are  cut  out  by  punch- 
ing overlapping  holes,  thus  leaving  a  ragged  edge  which  is 
afterwards  chipped  smooth.  The  plate  is  not  entirely  cut  away 
at  such  large  openings,  but  the  piece  to  be  removed  is  left 
hanging  at  three  or  four  places  until  after  the  plates  are  rolled 
into  cylindrical  form.  If  the  pieces  were  removed,  there  would 
be  less  resistance  to  the  rolls  at  such  places  and  the  plates 
would  have  a  conical  form  instead  of  a  true  cylindrical  form. 

The  punches  resemble  the  shears  shown  by  Fig.  155,  with 
a  punch  and  die  instead  of  the  knives.  Machines  are  often  so 
made  that  they  either  punch  or  shear. 

Planing. — After  the  plate  is  sheared  and  punched  the 
edges  are  planed  to  a  slight  angle  to  give  a  good  calking 
edge. 

The  planer  shown  by  Fig.  156  has  a  long  narrow  bed  on 
which  the  edge  of  the  plate  is  laid  and  to  which  it  is  clamped 
by  a  follower;  the  follower  is  forced  down  by  screws  which 
pass  through  a  beam  as  shown.  The  tool-carriage  is  drawn- 
back  and  forth  by  a  leading-screw ;  the  tool  is  made  to  cut  on 
both  strokes,  and  is  fed  by  hand  between  the  cuts. 

Scarfing. — When  the  plates  are  joined  by  a  lap-joint  the 
proper  corners  of  each  plate  are  heated  in  a  portable  forge 
near  the  planer,  and  are  drawn  down  or  scarfed  so  that  the 
overlapping  plates  may  come  close  together  and  not  leave  a 
space. 

Plate-rolls. — The  plates  for  forming  the  cylindrical  shell 
are  bent  to  shape  cold  by  running  them  through  bending-rolls 
The  horizontal  roll  represented  by  Fig.  157  has  two  parallel 
rolls  below  that  are  driven  in  the  same  direction  by  gearing. 
The  upper  roll  is  adjusted  at  each  end  separately,  and  some 
care  is  required  or  the  shell  will  receive  a  conical  shape  instead 
of  a  true  cylindrical  shape.      The  bearing  at  one  end  of  the 


SHOP-PRACTICE. 


3*5 


316 


STEAM-BOILERS. 


SHOP-PRACTICE. 


3*7 


roil  can  be  swung  out,  as  shown  by  the  figure,  to  remove  the 
plate  after  it  is  rolled. 

The  rolls  may  be  driven  in  either  direction  by  crossed  and 
open  belts.      The  plate  to  be  rolled  has  one  edge   introduced 


Fig.  is* 


between  the  upper  and  lower  rolls,  the  upper  roll  is  brought 
down  and  the  rolls  are  started  up.  The  plate  is  run  through 
nearly  to   the  other  edge    then  the  top  roll  is  screwed  down 


3 1 3  STEA  M -BOILERS. 

farther  and  the  rolls  are  reversed.  Thus  the  plate  is  run  back 
and  forth  and  the  top  roll  is  gradually  drawn  down  till  the 
plate  acquires  the  proper  form. 

The  extreme  edges  of  the  plate  are  not  bent  in  this  process: 
they  are  commonly  bent  afterwards  by  hammering  them  with 
sledges.  Some  rolls  have  a  special  device  for  bending  the 
edges;  it  consists  of  two  short  overhanging  rolls  about  fifteen 
inches  long,  one  concave  and  the  other  convex.  The  ends  of 
the  plate  are  fed  through  these  rolls  sideways,  and  are  bent 
before  they  are  introduced  into  the  long  rolls. 

Vertical  rolls,  shown  by  Fig.  158,  are  coming  into  use  in 
boiler-shops.  They  take  up  less  floor-space,  and  the  plate  after 
it  is  rolled  up  into  cylindrical  form  is  easily  hoisted  off  from 
the  front  roll.  For  this  purpose  the  front  roll  is  counterbal- 
anced and  the  top  end  can  be  swung  out  clear  from  the  hous- 
ing. The  figure  shows  the  rolls  as  erected  by  the  builders; 
in  the  boiler-shop  the  plate  at  the  lower  end  of  the  rolls  is 
flush  with  the  floor  of  the  boiler-shop. 

The  width  of  plate  that  can  be  rolled  by  either  horizontal 
or  vertical  rolls  depends  on  the  length  of  the  rolls,  The 
length  of  the  rolls  and  the  reach  of  the  riveter  (to  be  men- 
tioned later)  determine  the  width  of  plate  that  can  be  handled 
in  the  shop. 

Assembling  and  Riveting. — When  the  plates  for  a  boiler 
have  been  punched,  planed,  and  rolled  they  are  assembled  in 
courses,  and  bolted  together  ready  for  riveting.  Formerly 
boilers  were  commonly  punched  and  riveted  ;  now  it  is  cus- 
tomary to  punch  the  rivet-holes  one  eighth  of  an  inch  smaller 
than  the  finished  size  and  then  drill  to  the  right  size  after  the 
boiler  is  assembled.  This  is  more  expeditious  than  drilling 
directly,  and  as  all  the  metal  affected  by  punching  is  removed 
it  gives  as  good  results.  It  is  the  custom  in  most  shops  to 
drill  the  holes  out  at  the  riveting-machine  immediately  before 
the  rivets  are  driven  and  thus  each  rivet-hole  is  sure  to  be 
true. 


SHOP-PRACTICE.  319 

The  shells  of  heavy  marine  boilers  arc  drilled  after  the 
plates  are  assembled  without  previous  punching.  A  few  holes 
are  drilled  before  the  plates  are  rolled  and  serve  for  bolting 
the  plates  in  place  when  the  boiler  is  assembled.  There  are 
two  forms  of  machines  for  drilling  marine-boiler  shells.  In  one 
the  boiler  is  placed  horizontal  on  rollers  so  that  it  may  be 
readily  turned,  There  are  two  or  three  upright  frames  each 
carrying  a  drill.  The  frames  may  be  adjusted  lengthwise  of 
the  boiler,  and  the  drills  may  be  set  at  any  height  or  turned  at 
an  angle.  When  a  longitudinal  seam  is  drilled  the  boiler  is 
rotated  to  bring  a  row  of  rivets  to  a  drill,  and  the  frame  is  trav- 
ersed from  hole  to  hole.  When  a  ring-seam  is  drilled  the 
drill  is  brought  to  the  proper  place,  and  the  boiler  is  rotated  so 
as  to  bring  the  rivet-holes  in  succession  to  the  drill.  The 
other  machine  has  the  boiler  placed  on  one  end  and  the  verti- 
cal frames  carrying  the  drills  can  be  rotated  into  place,  and  the 
boiler  can  be  turned  on  a  vertical  axis. 

If  plates  are  punched  and  riveted  without  drilling,  the 
holes  should  be  punched  from  the  side  of  the  plate  which 
comes  in  contact  with  the  other  plate.  The  reason  for  this 
is  that  the  die  is  always  a  little  larger  than  the  punch  and  the 
hole  is  slightly  conical,  larger  at  the  side  where  the  die  holds 
up  the  plate.  If  the  smaller  ends  of  the  holes  in  two  plates 
are  brought  together,  then  the  rivet  fills  the  hole  better  ami 
draws  the  plates  up  more  perfectly  as  the  rivet  cools.  It  is 
clear  that  three  or  more  overlapping  plates  should  always  be 
drilled,  as  punched  holes  cannot  always  be  brought  together  in 
a  proper  manner.  This  is  aside  from  the  desirability  of  drill- 
ing all  rivet-holes. 

Returning  now  to  the  assembling  of  a  cylindrical  boiler, 
the  process  is  as  follows:  The  back  head  is  put  in  the  rear 
course  or  ring  of  the  shell,  and  is  bolted  with  six  or  eight  bolts 
through  the  punched  holes.  The  head  and  ring  are  hoisted 
up  to  the  drill  near  the  riveter,  and  six  or  eight  holes  are 
drilled  at  about  equal  distances  around  the  seam  holding  the 


320  STEAM-BOILERS. 

head  into  the  ring  or  course,  and  rivets  are  driven  by  the 
machine  in  these  holes.  The  bolts  are  now  taken  from  the 
punched  holes,  and  all  the  remaining  holes  arc  drilled  and 
riveted,  completing  the  ring-seam  through  the  flange  of  the 
back  head.  The  reason  for  driving  a  few  rivets  first,  at  equal 
intervals,  is  that  the  errors  of  spacing,  when  any  exist,  are 
distributed,  and  are  removed  during  the  subsequent  drilling; 
while  such  errors  might  accumulate  and  give  trouble  if  the 
seam  were  riveted  in  succession  beginning  at  one  point, 
without  first  driving  a  few  rivets  at  intervals. 

After  the  ring-seam  through  the  flange  of  the  head  is 
completed,  the  longitudinal  seam  or  seams  are  drilled  and 
riveted.  Here  again  a  few  rivets  are  driven  at  intervals 
before  the  seam  is  riveted  up.  A  few  holes  at  the  ends  of 
the  seams  are  left  for  convenience  in  joining  onto  the  next 
course. 

The  head  and  first  course  are  now  lowered  onto  the  next 
course,  which  has  been  assembled  in  readiness.  A  few  bolts 
are  put  through  the  punched  holes,  and  the  two  courses  are 
hoisted  up,  drilled  and  riveted  in  the  way  already  described 
for  the  rear  course. 

When  all  the  courses  are  riveted  together  the  front  head 
is  put  in  with  the  flange  out  so  that  the  rivets  in  that  flange- 
can  be  driven  on  the  machine.  The  closing  seams  on  a  boiler 
which,  like  the  Scotch  boiler,  has  both  heads  set  with  the 
flange  in,  must  be  riveted  by  hand. 

Rivets  are  heated  in  a  small  forge  near  the  riveter  and 
are  passed  to  a  man  inside  the  boiler,  who  picks  them  up  in 
tongs,  thrusts  them  through  the  holes  from  within  and  guides 
the  head  of  a  rivet  up  to  the  die  which  is  inside  the  boiler. 
Sometimes  the  rivets  are  thrust  through  from  without,  in 
which  case  the  man  inside  the  boiler  guides  the  point  to  the 
die.  On  the  platform  of  the  machine  stand  the  riveter  and 
two  or  three  helpers.  They  adjust  the  boiler  so  that  the 
rivet  is  brought  between  the  dies,  and  the  riveter  pulls  the 


SHOP-PRACTICE. 


32I 


lever  which  controls  the  ram,  and  the  outer  die  is  driven 
against  the  rivet,  forming  the  head  and  closing  up  the  rivet 
in  the  joint. 

The  holes  are  drilled  about  one  sixteenth  of  an  inch  larger 
than  the  rivets.  The  pressure  of  the  dies  varies  from  20  to 
70  tons,  depending  on  the  thickness  of  the  plate;  enough  to 
compress  the  rivet  and  fill  the  hole  completely.  The  rivets, 
as  they  cool,  shrink  and  draw  the  plates  firmly  together. 

Riveting-machines. — There  are  four  types  of  riveting- 
machines  used  for  boiler-work,  depending  on  the  method  of 
moving  the  ram  or  plunger  which  carries  the  movable  die. 
The  motion  may  be  derived  from — 

1.  A  cam  and  toggle. 

2.  A  hydraulic  cylinder, 

3.  A  combination  of  a  hydraulic  cylinder  with  a  cam  and 
toggle. 

4.  A  steam-cylinder. 

The  cam  and  toggle  riveter  is  now  seldom  used.  In  it 
the  ram  carrying  the  movable  die  is  driven  by  a  toggle-joint 
that  is  closed  by  a  cam,  which  in  turn  is  driven  by  a  belt  and 
gearing.  The  adjustment  for  different  thicknesses  of  plate  is 
made  by  a  wedge  behind  the  ram,  which  can  be  set  bv  aid  of 
a  screw.  The  pressure  on  the  rivet  is  controlled  by  the  elas- 
ticity of  the  frame  of  the  machine  and  the  setting  of  the 
wedge  ;    it  cannot  be  regulated  satisfactorily. 

The  hydraulic  riveter,  in  one  form  or  another,  is  most  com- 
monly used  at  the  present  time.  With  it  a  definite  pressure 
can  be  applied  to  each  rivet  whatever  the  thickness  of  plate. 
Fig.  159  represents  a  hydraulic  riveter  with  a  reach  of  96 
inches  which  can  apply  a  pressure  of  150  tons.  It  consists 
essentially  of  two  heavy  cast-iron  levers  or  beams,  bolted 
together  near  the  middle  and  at  the  lower  end.  One  beam 
carries  the  fixed  die  at  its  upper  end  ;  the  other  carries  the 
ram  and  hydraulic  cylinder.  The  stroke  of  the  ram  can  be 
adjusted  and  is  controlled  by  a  single  lever.      The  ram  moves 


322 


STEAM-BOILERS. 


in  straight  girders,  and  may  apply  an  eccentric  pressure  with- 
out rotating  or  springing. 

Some  hydraulic  riveters  have  a  hydraulic   closing  device 


Fig.  159. 
for  holding  the  plates  together  while  the  rivets  are  driven. 
Even  when  furnished  it  is  commonly  not  used. 

The  reach  of  a  riveting-machine  is  the  distance  from  the 
dies  to  the  bed-plate  at  the  middle  of  the  machine.  It  limits 
the  width  of  plate  that  can  be  riveted  by  the  machine. 

A  portable  hydraulic  riveter  is  shown  by  Fig.  160,  which 
has  a  reach  of  12  inches  and  can  apply  a  pressure  of  75  tons. 


SHOP-PRACTICE. 


323 


It  can  be  swung  into  position  by  a  crane  and  can  be  turned  to 
any  angle  by  the  gear  at  the  trunnion.  This  type  of  ma- 
chine is  used  largely  for  bridgework;  it  is  sometimes  used 
for  riveting  nozzles,  manhole-rings,  brackets,  and  reinforcing- 
plates  onto  boilers. 

The  power  for  working  a  hydraulic  riveter  is  derived  from 
either  a  steam-pump  or  a    power-pump.      A    heavy  geared 


Fig.  100. 
power-pump  is  shown  by  Fig.  161;  it  is  run  continuously 
and  delivers  water  to  an  accumulator  from  which  water  is 
supplied  to  the  hydraulic  cylinder  which  moves  the  ram. 
The  accumulator  consists  essentially  of  a  loaded  piston  or 
plunger.      Water  is   pumped   into  the   cylinder  of  the  accu- 


3  24 


STEAM-BOILERS 


mulator,  and  is  drawn  out  by  the  hydraulic  cylinder  as  needed. 
When  Ihe  accumulator  reaches  the  end  of  its  stroke  it  closes 
a  valve  on  the  pipe  from  the  pump  so  that  it  receives  no 
more  water;  at  the  same  time  it  opens  a  by-pass  from  the 
delivery  to  the  suction  of  the  pump  which  continues  to  runs 
but  has  at  that  time  v^ery  little  resistance  to  overcome.     When 


Fig.  161. 

some  water  has  been  withdrawn  from  the  accumulator  the  by- 
pass is  closed  and  the  valve  on  the  delivery-pipe  is  opened. 
When  a  steam-pump  is  used  there  is  a  device  for  shutting  off 
steam  from  the  pump  when  the  accumulator  is  near  the  end  of 
its  stroke,  and  letting  it  on  again  when  more  water  is  required. 
An  accumulator,  shown  by  Fig.  162,  is  loaded  by  scrap- 
iron  in  a  plate-iron  cylinder.     Inside  the  plate-iron  cylinder  is 


SHOP-PRACTICE. 


325 


a  cast-iron  cylinder  which  is  closed  at  the  top  and  which  moves 
on  a  fixed  plunger.  This  plunger  passes  through  a  stuffing- 
box  and  is  carried  by  a  cast-iron  bed-plate.     When  water  is 


Fig.  162 


pumped  into  the  cylinder  through  a  passage  in  the  fixed 
plunger,  the  whole  weight  of  the  cylinder,  plate-iron  casing, 
and  scrap-iron  load  are  lifted.      The  pressure  required  to  do 


326 


STEAM-BOILERS 


this  depends  on  the  load ;  it  is  the  pressure  which  is  exerted 
on  the  plunger  of  the  hydraulic  cylinder  moving  the  ram. 
The  frame  of  I  beams  at  the  sides  forms  a  guide  for  the 
accumulator-cylinder  and  its  load. 

Another  form  of  accumulator,  loaded  with  heavy  cast-iron 
blocks  and  without  any  exterior  guides,  is  shown  by  Fig.  163. 


Fig.  16?. 


The  hydraulic  riveter  with  toggle  and  cam  combines  the 
simplicity  of  the  cam-and-toggle  machine  with  the  advantage 
of  a  definite  and  determinable  pressure  on  the  rivet,  which  is 
the  best  feature  of  the  hydraulic  machine.  The  toggle  bears 
against  the  ram  at  the  front  end,  and  against  the  plunger  of  a 
hydraulic  cylinder  at  the  back  end.  The  cylinder  is  connected 
with  an  accumulator  which  is  loaded  to  give  the  desired  pres- 
sure on  the  rivet.     Suppose  that  pressure  to  be  30  tons;    then 


SHOP-PRACTICE.  327 

when  the  cam  closes  the  toggle,  the  rear  end,  resting  against 
the  hydraulic  plunger,  remains  at  rest,  and  the  tront  end 
drives  the  ram  and  compresses  the  rivet  till  a  pressure  of  30 
tons  is  reached.  When  that  pressure  is  reached  the  hydiaulic 
plunger  yields,  forces  water  into  the  accumulator  ana  raises 
the  load  on  it.  When  the  cam  releases  the  toggle,  th 
draulic  plunger  moves  forward  and  the  load  on  the  accui. 
tor  falls  and  drives  water  into  the  cylinder.  The  stroke  of 
the  hydraulic  plunger  may  be  very  snort,  as  the  principal  part 
of  the  stroke  of  the  ram  is  made  before  the  piunger  yields. 
There  is  no  loss  of  water  except  by  leakage,  which  may  be 
made  up  from  time  to  time  by  a  hand-pump.  This  machine 
gives  a  definite  pressure  on  the  rivet  whatever  the  thickness 
of  the  plate,  like  the  plain  hydraulic  riveter.  It  has  no  pump 
and  the  accumulator  is  smaller.  If  the  plunger  has  a  large 
area,  the  load  on  the  accumulator  need  not  be  very  great. 

Hand-riveting. —  In  a  modern  boiler-shop  almost  all  the 
riveting  is  done  by  machine  because  it  is  cheaper  and,  espe- 
cially on  heavy  work,  is  more  likely  to  be  well  done.  There 
are,  however,  a  good  many  rivets  on  any  boiler  that  must  be 
driven  by  hand.  In  such  case  the  rivet,  which  may  be  heated 
entirely  or  at  the  point  only,  is  thrust  through  the  hole  from 
within  and  is  held  up  by  a  man  inside,  who  has  for  this  pur- 
pose a  hammer  or  weight  which  weighs  about  20  pounds  on  a 
long  handle.  He  has  also  an  iron  hook  which  he  hooks  into 
a  rivet-hole,  and  against  which  he  gets  a  purchase  to  hold  the 
rivet  up  while  it  is  driven.  Two  men  with  hammers  that 
weigh  about  5  pounds  drive  the  rivet,  striking  in  turn.  A  few 
heavy  blows  are  struck  to  close  the  joint  and  partially  form 
the  head,  then  the  head  is  finished  in  the  shape  of  a  straight- 
sided  cone  with  lighter  hammers.  If  the  rivet  is  long  enough 
to  form  a  good  head,  and  if  it  is  driven  with  care  and  skill, 
hand-riveting  may  be  equal  to  machine-riveting.  If  the  heads 
are  ill-formed,  or  if  they  are  too  low,  the  work  may  be  very 
inferior. 

Snap-riveting. — This  method  of  riveting,  which  is  espe- 


328  STEA  M-BOIL  ERS. 

cially  convenient  for  driving  rivets  in  contracted  spaces,  has 
some  resemblance  to  machine-riveting.  The  rivet  is  thrust 
through  the  hole  and  held  up  from  within  the  boiler.  The 
joint  is  closed  and  the  head  is  roughly  formed  by  a  few  blows 
of  a  heavy  hammer,  then  a  snap  or  die  is  held  on  the  rivet 
and  driven  with  sledge-hammers.  For  large  rivets  the  sec- 
tion of  the  snap  should  be  a  parabola,  and  the  head  should  be 
relatively  small  in  diameter  and  high,  because  this  form  causes 
the  rivet  to  fill  the  hole  better  and  makes  sounder  work. 

Tube-expanders.— The  tubes  are  expanded  into  the  tube- 
sheets  to  make  a  steam-tight  joint,  beginning  a.;  the  least  acces- 
sible end.  They  are  commonly  a  little  too  long  ana  are  cut 
off  at  the  projecting  end  by  a  tube-cutter.  The  tubes  extend 
through  the  heads  a  slight  amount,  and  are  beaded  over,  after 
they  are  expanded,  by  a  special  tool.  The  expanders  most 
commonly  used  are  known  as  the  Prosser  and  the  Dudgeon 
expanders. 

The  Prosser  expander,  represented  by  Fig.  164,  is  made  up 


Fig.  16.;. 
of  a  number  of  steel  segments  held  in  place  by  a  spring  on  a 
cylindrical  extension  of  the  segments.  The  acting  part  of  the 
segments  have  the  form  to  be  given  to  the  tube  after  it  is 
expanded.  The  inside  of  the  segments  forms  a  straight  hol- 
low cone  into  which  a  steel  taper  pin  fits.  The  expander  is 
forced  into  the  tube  and  is  expanded  by  driving  in  the  pin 
with  a  hammer.  This  should  be  done  gradually  so  as  not  to 
distress  the  metal  of  the  tube  too  much,  and  the  expander 
should  be  frequently  slacked  back  and  shifted  part  way  round 
on  account  of  the  spaces  between  tne  segments. 


SHOP-PRACTICE. 


329 


The  Dudgeon  expander,  Pig.  165,  has  a  set  of  rolls,  three  or 
more,  in  a  frame.  The  rolls  are  forced  out  against  the  sides 
of  the  tube  by  driving  in  a  taper  pin.     The  pin  and  frame  are 


Fig.  165. 

rotated  as  the  pin  is  driven,  and  the  rolls  gradually  force  the 
tube  against  the  tube-plate. 

Fig.  166  shows  a  self-feeding  tube  expander  of  the  same  type 
as  the  Dudgeon. 


Fig.  166. 


Although  the  two  expanders  accomplish  much  the  same 
result,  the  action  is  different.  The  Prosser  causes  an  abrupt 
stretching  of  the  tube  while  the  Dudgeon  rolls  the  tube  out  grad  • 
ually.     One  expander  seems  to  be  as  good  as  the  other. 

The  expanded  end  of  the  tube  conforms  to  the  shape  of  the 
segments  of  the  Prosser  expander  or  to  the  shape  of  the  rolls 
used  in  the  Dudgeon.  In  general,  the  tube  ends  expanded  by 
the  two  expanders  will  appear  as  in  Figs.  167  and  168,  which  are 
drawn  out  of  proportion  to  show  the  difference  more  clearly. 

An  inexperienced  person  who  may  be  using  a  tube  expander 
for  the  first  time  may  judge  when  a  tube  has  been  expanded 
sufficiently  to  be  tight  by  watching  the  plate  around  the  tube* 


33° 


STEAM-BOILERS. 


to  see  when  fine  hair-like  cracks  appear  in  the  scale  which  covers 
the  outside  of  the  plate. 

When  these  lines  show  it  means  that  the  tube  has  been  made 
to  fill  the  hole  and  that  the  hole  has  begun  to  be  stretched. 

After  the  tubes  are  expanded  the  ends  are  beaded  over  by  a 
special  tool  known  as  a  boot -tool. 

Beading  adds  a  little  to  the  holding  power  of  a  tube.  Tube 
ends  which  are  directly  over  a  furnace,  as  is  the  case  in  vertical 


Fig.  167. 


Fig.  168. 


boilers  like  the  Manning,  should  always  be  beaded.  This  bead- 
ing keeps  the  end  of  the  tube  in  such  cases  from  being  eaten 
away  by  the  fire. 

A  vacuum  may  possibly  be  found  in  a  boiler,  if  it  is  allowed 
to  cool  without  admitting  air.  The  Prosser  method  has  an 
advantage  in  such  case,  when  the  tubes  act  as  struts  between 
the  heads.  The  Dudgeon  method  will  then  act  by  friction 
only.  The  rollers  might  be  shaped  to  give  an  expansion  just 
inside  the  plate,  instead  of  making  them  straight;  there  is, 
however,  no  evidence  of  trouble  from  this  source  in  practice. 


SHOP-PRACTICE 


33>i 


Calking. — The  riveted  seams  of  a  boiler  are  made  steam- 
tight  by  calking,  which  consists  in  driving  the  lower  part  of 
the  planed  edge  forcibly  against  the  plate  beneath.  Fig.  169 
shows  the  form  of  calking-tool  used  in  hand-calking,  the  posi- 


Fig.  169. 

tion  in  which  it  is  held,  and  the  way  the  extreme  edge  of  the 
plate  is  compressed  against  the  plate  beneath.  The  acting  sur- 
face of  the  tool,  which  is  about  an  men  wide,  is  ground  at  an 
angle  of  somewhat  less  than  900,  and  the  edge  is  rounded 
slightly  so  that  it  will  not  cut  the  lower  plate.  The  tool  is  slid 
along  the  under  plate  against  the  edge  of  the  upper  plate  and 
struck  with  a  hammer.  If  the  tool  is  ground  to  a  sharp  edge 
and  used  carelessly,  a  groove  may  be  cut  in  the  under  plate 
and  serious  injury  may  be  done. 

A  pneumatic  calking-machine  or  tool  is  now  used  for 
doing  most  of  the  calking  in  boiler-shops.  In  general  prin- 
ciple it  resembles  a  rock-drill,  and  consists  of  a  cylinder  in 
\Vfiich  works  a  piston  and  rod  on  the  end  of  which  is  the 
calking-tool.  Air  is  supplied  for  working  the  piston,  at  a 
pressure  of  60  or  80  pounds,  through  a  flexible  tube.  It 
makes  about  1500  working-strokes  a  minute,  3/16  of  an  inch 
long.  The  ca'lker,  which  is  about  2\  inches  in  diameter  out- 
side and  15  inches  long  over  all,  is  held  by  a  workman  who 
presses  it  slowly  along  the  seam  to  be  calked.  The  edge  of 
the  tool  is  well  rounded  so  as  not  to  injure  the  lower  plate. 


332  STEAM-BOILERS. 

Work  can  be  done  four  times  as  rapidly  with  the  pneumatic 
calker  as  by  hand. 

Cold-water  Test. — After  the  boiler  is  calked  it  is  tested 
to  about  once  and  a  half  the  working  pressure,  with  cold 
water.  During  the  test  the  boiler  is  carefully  watched  to 
detect  any  notable  change  of  shape  or  other  sign  of  faulty 
design  or  construction,  and  important  leaks  are  marked ; 
small  leaks  are  of  no  consequence,  as  they  will  fill  up  with 
rust.  Important  leaks  must  be  calked  after  the  pressure  is 
relieved;  if  necessary,  pressure  may  be  applied  again  to  see  if 
they  are  stopped. 

If  the  boiler  is  examined  by  a  boiler-inspector,  he  makes 
his  inspection  before  the  boiler  is  painted,  and  stamps  certain 
letters  on  the  head  or  over  the  fire-door  to  show  that  the 
boiler  has  passed  inspection. 

Finally  the  boiler  is  painted  and  oiled  ready  for  shipping. 


CHAPTER  XI. 
BOILER-TESTING. 

The  main  object  of  a  boiler-test  is  to  determine  the 
amount  of  water  evaporated  per  pound  of  coal,  or,  more  ex- 
actly, the  amount  of  heat  transferred  to  the  boiler  per  pound 
of  coal  burned.  For  this  purpose  it  is  necessary  to  deter- 
mine : 

i.  The  number  of  pounds  of  water  pumped  into  the  boiler 
during  the  test. 

2.  The  number  of  pounds  of  coal  burned,  and  the  weight 
of  ashes  left. 

3.  The  temperature  of  the  feed-water  when  it  enters  the 
boiler. 

4.  The  pressure  of  the  steam  in  the  boiler. 

5.  The  per  cent  of  moisture  in  the  steam  discharged  from 
the  boiler. 

It  is  desirable  to  determine  the  conditions  of  combustion, 
such  as  the  draught,  the  weight  of  air  supplied  per  pound  of 
coal,  the  composition  of  the  products  of  combustion,  and  the 
temperature  of  the  escaping  flue-gases.  It  is  also  desirable  to 
have  determinations  made  of  the  composition  of  the  coal  and 
its  total  heat  of  combustion,  but,  as  was  explained  in  Chapter 
II,  these  determinations  should  usually  be  intrusted  to  a 
chemist  and  to  a  physicist. 

"Water. — The  best  and  most  satisfactory  way  is  to  weigh 
the  feed-water  directly,  in  proper  tanks  or  barrels  on  scales. 
There  should  be  two  barrels  or  tanks  large  enough  so  that  the 
filling,  weighing,  and   emptying  may  proceed  without  haste. 

333 


334  STEAM-BOILERS. 

The  scales  should  be  adjusted  and  tested  with  a  standard 
weight  and  should  be  known  to  be  correct  and  sensitive. 
Good  commercial  platform  scales  are  sufficient  for  this  pur- 
pose. 

The  weighing-barrels  should  be  placed  high  enough  to 
discharge  into  a  tank  or  reservoir  from  which  the  feed-water 
is  drawn  by  a  pump  or  injector.  This  tank  should  hold  more 
than  both  weighing-barrels,  so  that  when  it  is  about  half 
empty  an  entire  barrelful  of  water  may  be  discharged  into  it 
without  danger  of  overfilling  it  and  wasting  water.  The  bar- 
rels are  emptied  through  large  quick-opening  lever-valves; 
this  point  should  receive  attention,  as  any  delay  caused  by 
small  valves  is  very  annoying. 

The  weighing-barrels  are  filled  either  from  a  water  system 
or  by  a  special  pump  from  a  well  or  reservoir.  When  a  direct- 
acting  steam-pump  is  used,  a  quarter-inch  by-pass  should  be 
carried  from  the  delivery-pipe  to  the  suction-pipe;  the  pump 
will  then  run  slowly  when  the  valves  on  the  pipes  leading  to 
the  weighing-barrels  are  shut ;  when  one  of  these  valves  is 
opened  the  pump  starts  away  promptly,  and  it  slows  down 
again  when  the  valve  is  shut.  If  a  power-pump  is  used,  it 
may  be  convenient  to  arrange  so  that  it  shall  run  all  the  time 
at  full  power,  discharging  into  the  well  or  reservoir  when, 
neither  barrel  is  filling. 

Weighing  water,  though  simple  enough,  requires  care  and 
.intelligence,  as  any  blunder  will  spoil  the  test.  The  observer 
should  proceed  systematically.  He  will  naturally  start  with 
both  barrels  filled,  weighed  and  recorded  before  the  test 
begins.  When  the  level  in  the  feed-tank  has  fallen  so  that  it 
can  receive  a  barrelful  of  water  he  will  open  the  discharge- 
valve  from  one  barrel,  which  should  be  marked  and  designated 
as  Barrel  No.  i.  When  that  barrel  is  emptied,  he  will  close 
tho  valve  and  weigh  the  barrel ;  the  weight  empty  is  set  down 
and  subtracted  from  the  weight  full  to  get  the  weight  dis- 
chaf^ed.      The   record    of    weights    is   kept    in    a    table    con- 


BOILER-TESTING.  335 

taining  columns  for  the  name  of  the  barrel,  weights  full, 
weights  empty,  weights  discharged,  and  time  at  which  dis- 
charged. The  weight  of  the  barrel  empty  must  be  taken 
each  time,  as  the  barrel  will  not  drain  completely  in  the  time 
that  can  be  allowed. 

Water  may  now  be  turned  on  to  fill  Barrel  No.  I,  and 
Barrel  No.  2  may  be  emptied,  as  occasion  demands.  Then 
one  barrel  may  be  filling  when  the  other  is  emptying,  and  the 
work  may  proceed  rapidly  but  without  confusion.  The  errors 
that  a  novice  is  liable  to  are  either  to  forget  to  record  the 
weight  of  a  barrelful  of  water,  or  to  empty  a  barrel  that  lias 
not  been  weighed. 

It  is  convenient  and  almost  necessary  to  have  some  sort  of 
an  index  or  telltale  to  show  the  water-weigher  where  the 
water-level  is  in  the  feed-tank.  For  this  purpose  we  may  use 
a  float,  with  a  string  that  runs  up  over  a  pulley  and  is  kept 
taut  by  a  small  weight  moving  over  a  scale,  which  is  placed 
in  front  of  the  weighing-barrels.  This  float  is  not  used  to 
determine  the  level  of  the  water  in  the  feed-tank  at  the  begin- 
ning and  end  of  the  test. 

At  the  beginning  of  the  test  the  level  of  the  water  in  the 
feed-tank  is  marked,  and  at  the  end  of  the  test  the  level  is 
brought  to  the  same  mark,  so  that  all  the  water  delivered  by 
the  weighing-barrels  is  drawn  out  of  the  feed-tank  by  the 
feed-pump.  A  good  way  of  marking  the  water-level  is  to 
fasten  to  the  side  of  the  tank  a  piece  of  wire  bent  into  a  hook, 
with  its  point  projecting  slightly  above  the  water-level.  This 
hook  will  commonly  be  placed  in  position  before  the  test 
begins,  and  the  tank  will  be  filled  up  to  the  level  so  marked 
before  water  is  drawn  from  the  feed-tank. 

If  water  cannot  be  weighed  directly,  it  may  be  measured 
in  tanks  of  known  capacity  which  are  alternately  filled  and 
emptied.  Or  the  water  may  be  measured  by  a  good  water- 
meter,  which  must  be  tested  under  the  conditions  of  the  test 
to  determine  its  error.     Care  must  be  taken  to  keep  the  meter 


336  STEAM-BOILERS. 

free  from  air  or  it  will  record  more  than  the  amount  of 
water  which  actually  passes.  Boiler-tests  on  steamships  can 
scarcely  be  made  without  using  meters. 

At  the  time  when  the  test  begins,  the  water-level  is  noted 
at  the  water-glass,  and  at  the  end  of  the  test  the  water-level 
is  brought  to  the  same  place.  The  best  way  is  to  fix  a 
wooden  scale  near  the  water-glass  and  record  the  height  of  the 
water  above  an  arbitrary  point  on  the  scale.  Sometimes  a 
string  is  tied  around  the  glass  at  the  water-level  when  the  test 
is  started;  in  such  case  the  distance  of  the  string  from  some 
fixed  point  on  the  fittings  of  the  water-glass  must  be  recorded, 
so  that  the  string  can  be  replaced  if  it  happens  to  be  moved 
or  if  the  glass  tube  breaks.  If  the  water  is  not  brought 
exactly  to  the  same  level  at  the  end  as  at  the  beginning  of  the 
test,  the  difference  is  noted  and  allowance  is  made.  It  has 
already  been  pointed  out  that  the  apparent  height  of  the 
water  depends  to  a  certain  extent  on  the  rate  of  vaporization 
and  on  the  rapidity  of  circulation  in  the  boiler;  consequently 
the  boiler  must  be  making  steam  at  the  same  rate  at  the  times 
when  the  water-level  is  observed  for  beginning  and  ending  the 
test. 

All  pipes  leading  water  to  or  from  the  boiler,  except  the 
feed-pipe,  must  be  disconnected.  Steam  may  be  taken  for 
any  purpose  and  through  any  pipe,  so  far  as  the  boiler-test  is 
concerned. 

Frequently  the  steam  used  by  an  engine  is  determined  by 
weighing  the  feed-water  for  a  boiler  which  is  used  exclusively 
for  that  engine.  If  the  boiler  is  fed  by  an  injector,  the  steam 
for  running  the  injector  should  be  taken  from  the  boiler,  for 
it  will  be  condensed  by  the  feed-water  and  returned  to  the 
boiler.  A  very  small  amount  of  the  heat  (less  than  two  per 
cent)  in  the  steam  supplied  to  an  injector  is  used  in  pumping 
the  feed-water;  the  remainder  is  used  in  heating  the  feed- 
water  and  is  returned  to  the  boiler.  The  temperature  of  the 
feed-water  must  be  taken  before  it  goes  to  the  injector.     If  the 


BOILER-TESTING. 


337 


boiler  is  fed  by  a  direct-acting  steam-pump,  that  pump  should 
be  run  with  steam  taken  from  some  other  source.  If  that 
cannot  be  done,  then  the  steam  used  by  the  pump  must  be 
determined  and  allowed  for,  unless  the  exhaust  from  the 
pump  can  be  turned  into  and  condensed  by  the  water  in  the 
feed-tank,  in  which  case  the  pump  is  in  the  same  condition 
as  an  injector.  The  best  way  of  determining  the  amount  of 
steam  used  by  a  steam-pump  is  to  condense  it  in  a  small  sur- 
face condenser,  and  to  collect  and  weigh  the  condensed  water. 
Or  the  steam  may  be  run  into  a  barrel  filled  with  cold  water, 
which  is  weighed  before  and  after  steam  is  run  in.  This 
method  requires  that  the  barrel  shall  be  emptied  when  the 
water  begins  to  vaporize,  and  filled  afresh  with  cold  water. 
Steam  used  by  a  calorimeter  for  determining  the  amount  of 
water  in  steam  must  be  ascertained  also;  the  methods  will  be 
given  in  connection  with  a  description  of  the  in-truments. 

Coal  and  Ash. — The  coal  required  during  a  boiler-test 
should  be  brought  in  as  required  in  barrows;  it  may  be  fired 
from  the  barrow  or  dumped  and  fired  from  the  Moor.  The 
barrow  should  be  weighed  full  and  empty,  and  the  difference 
should  be  recorded  together  with  the  time ;  the  latter  to  serve 
as  a  check  on  the  record  and  make  sure  that  a  barrow-load  is 
not  neglected.  The  weight  of  the  barrow  is  usually  the  same 
throughout  the  test.   Any  coal  left  unburned  is  weighed  back 

It  is  essential  that  the  condition  of  the  fire  shall  be  tne 
same  at  the  beginning  and  at  the  end  of  the  test.  There  are 
two  methods  in  vogue  for  trying  to  attain  this  result ;  if  the 
test  is  24  hours  long  or  more,  the  condition  of  the  fire  is  esti- 
mated by  its  appearance;  if  the  test  is  10  or  12  hours  long, 
the  test  is  started  and  stopped  with  the  grate  empty.  These 
are  for  tests  of  factory  boilers  with  a  combustion  of  15  to  20 
pounds  of  coal  per  square  foot  of  grate  per  hour.  For  tests 
on  marine  or  locomotive  boilers,  where  the  rate  of  combustion 
may  be  twice  or  five  times  as  rapid,  the  duration  of  a  test 
may  be  correspondingly  reduced. 


338  STEAM-BOILERS. 

Coal  in  solid  mass  will  weigh  70  or  80  pounds  to  the  cubic 
foot;  when  lying  on  a  grate  it  will  weigh  50  or  60  pounds. 
It  is  difficult  to  estimate  the  thickness  of  the  bed  of  coal  on  a 
grate  nearer  than  two  inches.  But  a  layer  of  coal  two  inches 
thick  will  weigh  8  or  10  pounds,  which  is  about  half  the  rate 
of  combustion  for  a  factory  boiler.  If  a  test  is  only  ten  hours 
long,  the  error  resulting  from  a  wrong  estimate  of  the  thick- 
ness of  the  fire  may  readily  be  five  per  cent.  If  the  test  lasts 
twenty-four  hours,  the  error  will  probably  not  be  more  than 
two  per  cent,  provided  a  proper  method  is  used. 

If  the  condition  of  the  fire  is  estimated  at  the  beginning 
and  end  of  the  test,  the  fire  should  be  cleaned  and  freed  from 
ashes  and  clinker  shortly  before  the  test  begins,  and  should 
then  be  spread  in  rather  a  thin  even  layer  of  clean  glowing 
coal.  Its  height  above  the  grate  should  be  estimated  with 
reference  to  some  mark  in  the  furnace  that  can  be  recognized 
readily.  Just  as  long  before  the  end  of  the  test  the  fire 
should  be  cleaned  and  levelled  in  the  same  manner,  and  the 
thickness  should  be  estimated  with  reference  to  the  mark 
chosen  at  the  beginning.  The  fireman  is  sure  to  have  a  clean 
bright  fire  at  the  beginning  of  the  test,  but  he  is  apt  to  have 
a  fire  with  much  the  same  appearance  that  is  half  clinker  at 
the  end.  The  error  from  estimation  may  be  very  serious  in 
such  case,  even  though  the  test  is  24  hours  long. 

If  the  test  is  started  and  stopped  with  the  grate  empty, 
the  boiler  must  be  brought  into  good  working  condition  about 
an  hour  before  the  test  is  to  start,  with  all  the  brickwork 
thoroughly  heated.  The  fire  is  allowed  to  burn  low,  and  the 
steam-pressure  is  maintained  by  reducing  the  draught  of 
steam  from  the  boiler.  Twenty  or  thirty  minutes  before  the 
test  starts,  the  fire  is  drawn  or  dumped  and  the  grate  and  ash- 
pit are  cleaned  out.  A  new  fire  is  started  with  wood,  and 
coai  is  thrown  on  as  soon  as  the  wood  is  well  alight.  The 
time  when  coal  is  thrown  on  is  counted  as  the  beginning  of 
the  test.      If  the  steam-pressure  falls  while  the  fire  is  drawn, 


BOILER-TESTING.  339 

the  stop-valve  may  be  nearly  or  quite  closed  to  keep  it  from 
falling  much  below  the  working-pressure.  Toward  the  end  of 
the  test  the  fire  is  allowed  to  burn  low,  and  at  the  end  of  the 
test  it  is  drawn  out  on  the  boiler-room  floor  and  quenched  with 
as  little  water  as  may  be,  not  enough  to  leave  it  wet.  The 
unburned  coal  is  picked  out  by  hand  and  weighed  back,  the 
clinker  and  ashes  are  separated  and  weighed  together  with  the 
clinker  withdrawn  during  the  test  and  the  ashes  in  the  ash-pit. 

If  any  appreciable  amount  of  coal  falls  through  the  grate, 
a  sample  from  the  ash-pit  may  be  picked  over  by  hand  to  es- 
timate the  proportions  of  unburned  coal  in  the  ash.  The  coal 
in  the  ash  is  allowed  for  in  calculating  the  per  cent  of  ash  in 
the  coal,  but  is  not  added  to  the  coal  weighed  back,  for  there 
is  no  way  of  burning  coal  thus  lost  through  the  grate.  When 
a  test  is  started  with  a  wood  fire,  more  or  less  coal  is  apt  to 
fall  through  the  grate  in  starting.  This  is  drawn  from  the  pit 
and  fired  over  again. 

It  is  customary  to  allow  the  fire  to  burn  low  before  draw- 
ing the  fire  at  the  end  of  the  boiler-test,  both  because  it  brings 
the  fire  more  nearly  to  the  condition  at  the  beginning,  and 
because  it  is  a  hard  and  unpleasant  job  to  draw  a  thick  fire. 
But  the  fire  should  be  maintained  at  its  normal  condition 
until  the  end  of  the  test  approaches,  and  should  be  a  good 
fire  when  drawn.  Extraordinary  results  may  be  obtained  by 
allowing  the  fire  to  burn  nearly  out  at  the  end  of  the  test,  a 
very  considerable  amount  of  steam  being  formed  by  heat 
given  out  by  the  boiler-setting.  It  is  unnecessary  to  say  that 
such  results  are  entirely  misleading. 

The  wood  used  for  starting  the  fire  is  weighed  and  allowed 
for  on  the  assumption  that  a  pound  of  wood  is  equivalent  to 
0.4  of  a  pound  of  coal.  The  total  weight  of  wood  used  is  not 
large. 

Temperature  of  Feed-water. — The  temperature  of  the 
feed-water  is  taken  by  a  thermometer  in  a  cup  filled  with  oil, 
screwed  into  the  feed-pipe  close  to  the  check-valve.      If  the 


34°  STEAM-BOILERS. 

temperature  varies,  it  may  be  read  every  five  minutes:  if  it 
is  found  to  be  steady,  less  frequent  intervals  will  do. 

Pressure  of  Steam. — The  steam-pressure  must  be  very 
nearly  the  same  at  the  beginning  and  end  of  a  test,  and 
should  remain  nearly  constant  throughout  the  test.  Read- 
ings are  commonly  taken  every  fifteen  minutes,  but  the  fire- 
man should  be  required  to  keep  the  pressure  nearly  constant 
at  all  times. 

The  steam-pressure  is  taken  by  a  spring-gauge  like  that 
shown  by  Fig.  108  on  page  269.  The  gauge  should  be 
compared  with  a  mercury  column  or  a  standard  gauge  both 
before  and  after  the  test,  and  a  correction  should  be  applied 
if  necessary.  If  the  pipe  carrying  pressure  to  the  gauge  fills 
up  with  water,  allowance  for  the  pressure  of  that  column  of 
water  must  be  made.  Each  foot  of  water  will  give  a  pressure 
of  about  0.43  of  a  pound  per  square  inch. 

The  reading  of  the  barometer  should  be  taken  two  or 
three  times  during  a  test.  The  reading  in  inches  of  mercury 
can  be  reduced  to  pounds  per  square  inch  by  multiplying  by 
the  weight  of  a  cubic  inch  of  mercury,  which  is  about  0.491 
of  a  pound. 

Very  commonly  the  pressure  of  the  steam  is  obtained 
indirectly  by  aid  of  a  thermometer  set  in  the  steam- pipe. 
The  absolute  pressure  corresponding  to  the  temperature  is 
then  obtained  from  a  table  of  the  properties  of  saturated 
steam.  The  thermometer  is  readily  standardized,  and  is  not 
so  likely  to  become  unreliable  as  a  steam-gauge. 

Most  vertical  boilers  and  some  water-tube  boilers  give 
superheated  steam ;  in  such  case  there  should  be  both  a 
thermometer  and  a  gauge  on  the  steam-pipe,  to  indicate  tem- 
perature and  pressure.  The  excess  of  the  temperature  by 
the  thermometer  above  that  corresponding  to  the  absolute 
pressure  of  the  steam,  as  found  in  a  table  of  properties  of 
steam,  is  the  degree  of  superheating. 

Specific  Heat  of  Superheated  Steam. — The  mean  value 


BOILER-TEST  IXC.  341 

of  the  specific  heat  of  superheated  steam  is  given  in  Chapter  II. 
The  value  is  commonly  represented  by  cp.  The  value  increases 
with  the  pressure  and  at  the  same  pressure  decreases  as  the  super- 
heat increases. 

For  example,  let  the  pressure  by  the  gauge  be  65.3 
pounds,  and  let  the  temperature  be  3500  F.  by  the  thermom- 
eter- The  absolute  pressure  corresponding  to  65.3  pounds 
is  80  pounds,  at  which  saturated  steam  has  the  temperature 
of  3 1 2 °.  1  F.      The  superheating  is  consequently 

3500  F.  -3i2°.i  F.  =  37°.9  F. 

The  heat  due  to  the  superheating  is 

0.53  X  3<S.2  =  20.1  R.  T.  U. 

When  the  steam  is  superheated,  the  formula  for  equivalent 
evaporation  is  changed  from  the  form  given  on  page  148  to 

cv\  /,  —  t)  +  r  +  q  —  q0 

ic'  7 , 

909.7 

in  which  ts  represents  the  actual  temperature  of  the  super- 
heated steam,  and  t  is  the  temperature  corresponding  to  the 
absolute  pressure  of  the  steam  determined  from  the  reading 
of  the  gauge. 

Priming. — A  boiler  which  has  sufficient  steam-space  and 
free  water- area  will  deliver  steam  which  contains  less  than 
two  per  cent  of  moisture. 

Professor  Denton  *  has  pointed  out  that  a  jet  of  steam 
blowing  into  the  air  from  a  petcock  will  give  a  characteristic 
blue  color  if  there  is  less  than  two  per  cent  of  water  in  the 
steam.  If  there  is  more  than  two  per  cent  of  moisture,  the 
jet  will  be  white.  Since  steam  seldom  contains  less  than 
one  per  cent  of  moisture  under  the  usual  conditions  of 
ordinary  practice,  it  is  possible  by  this  method  to  estimate 
the  condition  of  steam  with  a  probable  error  of  one  per  cent. 
*  Trans.  Am.  Soc.  Mech.  Engs.,  vol.  x.  p.  349. 


342 


STEAM-BOILERS. 


The  most  ready  way  of  determining  the  condition  of 
steam  is  by  the  aid  of  a  throttling-calorimeter,  devised  by 
Professor  Peabody,*  which  depends  on  the  fact  that  the  total 
heat  of  steam  increases  with  the  pressure,  so  that  dry  steam  be- 
comes superheated  when  the  pressure  is  reduced  by  throttling. 
If  the  steam  is  only  slightly  primed,  superheating  will  still 
take  place,  and  the  amount  of  priming  can  be  determined 
from  the  temperature  and  pressure  of  the  steam  after  it  is 
throttled.  If  there  is  much  moisture  in  the  steam,  it  fails  to 
superheat. 

A  good  form  of  this  apparatus  is  shown  by  Fig.  170, 
consisting  of  a  reservoir  A  to  which  the 
steam  to  be  tested  is  admitted  through 
a  half-inch  pipe  b  with  a  throttling-valve  ,. 
near  the  reservoir.  The  steam  flows 
away  through  an  inch  pipe  d.  At  f  is 
a  gauge  for  measuring  the  pressure,  and 
at  c  there  is  a  deep  cup  for  a  ther- 
mometer to  measure  the  temperature. 
The  boiler-pressure  may  be  taken  from 
a  gauge  on  the  main  steam-pipe  near 
the  calorimeter.  It  should  not  be  taken 
from  a  pipe  in  which  there  is  a  rapid 
flow  of  steam  as  in  the  pipe  b,  since 
the  velocity  of  the  steam  will  affect 
the  gauge-reading,  making  it  less  than 
tne  real  pressure.  The  reservoir  is 
wrapped  with  hair-felt  and  lagged  with  wood  to  reduce  radia- 
tion of  heat 

When  a  test  is  made  the  valve  on  the  pipe  d  is  opened 
wide  (this  valve  is  frequently  omitted),  and  the  valve  at  b  is 
opened  wide  enough  to  give  a  pressure  of  five  to  fifteen 
pounds  in   the   reservoir.      Readings   are   then   taken    of  the 


170. 


Trans.  Am.  Soc.  Mech.  Engs.,  vol.  x.  p.  327. 


bCILLK-TESTING. 


34j 


boiler-gauge,  of  the  gauge  at/,  and  of  the  thermometer  at  e. 
It  is  well  to  wait  about  ten  minutes  after  the  instrument  is 
started  before  taking  readings,  so  that  it  may  be  well  heated. 

The  method  of  calculation  can  be  readily  understood 
from  the  following 

Example. — The  following  are  the  data  of  a  test  made 
with  a  throttling  calorimeter: 

Pressure  of  the  atmosphere 14.8  pounds. 

Pressure  by  the  boiler-gauge 69.8        " 

Pressure  by  the  calorimeter-gauge....  12.0        " 

Temperature  in  the  calorimeter 268°.2  F. 

The  absolute  pressure  in  the  boiler  was 

69.8  -f-  14.8  =  84.6  pounds, 

at  which  the  heat  of  vaporization  is  896.8  B.  T.  U.  and  the 
heat  of  the  liquid  is  286.2  B.  T.  U.  So  that  with  x  part  of 
a  pound  steam  (and  1  —  x  priming1)  the  heat  in  one  pound  of 
moist  steam  was 

896. 8  x  +  286.2, 

in  which  x  was  to  be  determined.  The  absolute  pressure  in 
the  calorimeter  was 

12  +  14.8  =  26.8  pounds, 

at  which  the  temperature  was  243 °. 9  F.,  and  the  total  heat 
was  1 161.3  B.  T.  U.     The  heat  due  to  superheating  was 

o.55(268°.2  -  2430.9)  =  13.4  B.  T.  U., 

and  the  heat  in  one  pound  of  steam  in  the  calorimeter  was 

1 161. 3  +  13.4  =  1 174.7  B.  T.  I". 

But  the  process  of  throttling  neither  adds  nor  subtracts  heat, 
consequently 

896.8X  +  286.2  =  H74-7 
or         .v  =  0.990, 


344  STEAM-BOILERS. 

and  the  priming  was 

ioq(i  —  0.990)  =  1. 00  per  cent. 

The  calculation  can  be  conveniently  expressed  by  an  equa- 
tion in  which  r  and  q  are  the  heat  of  vaporization  at  the  abso- 
lute boiler-pressure,  and  A:  and  /,  are  the  total  heat  and  the 
temperature  at  the  absolute  pressure  in  the  calorimeter,  all 
taken  from  a  table  of  properties  of  steam  ;  while  tt  is  the 
temperature  of  the  superheated  steam  in  the  calorimeter. 
Then 

xr  +  q=Xi+cp(ta— h); 

li+cp(t,—ti)—q 

x  = 

r 

It  has  been  found  by  experiment  that  no  allowance  need 
be  made  for  radiation  from  the  calorimeter  if  made  as  de- 
scribed, provided  that  200  pounds  of  steam  are  run  through 
it  per  hour.  Now  this  quantity  will  flow  through  an  orifice 
one  fourth  of  an  inch  in  diameter  under  the  pressure  of  70 
pounds  by  the  gauge,  so  that  if  the  throttle-valve  be  replaced 
by  such  an  orifice  the  question  of  radiation  need  not  be  con- 
sidered. In  such  case  a  stop-valve  will  be  placed  on  the  pipe 
to  shut  off  the  calorimeter  when  not  in  use;  it  is  opened  wide 
when  a  test  is  made.  If  an  orifice  is  not  provided,  the 
throttle-valve  may  be  opened  at  first  a  very  small  amount 
and  the  temperature  in  the  calorimeter  noted  after  a  few  min- 
utes; the  valve  may  be  opened  a  trifle  more,  whereupon  the 
temperature  will  usually  rise,  showing  too  little  steam  used. 
Jf  the  valve  is  opened  little  by  little  till  the  temperature  stops 
rising,  it  will  then  be  certain  that  enough  steam  is  used  to 
reduce  the  error  from  radiation  to  a  very  small  amount. 

Various  modifications  of  the  throttling-calorimeter  have 
been  proposed,  mainly  with  a  view  of  reducing  its  size  and 
weight.  Almost  any  of  them  will  prove  satisfactory  in  prac- 
tice, but  some  will  be  found  to  be  liable  to  error  from  radia- 


BOILER-TESTING. 


345 


tion  or  from  the  fact  that  there  is  not  sufficient  opportunity 
for  the  steam  to  come  to  rest  and  properly  develop  the  super- 
heating due  to  throttling.  One  great  advantage  of  this 
instrument  is  that  ordinary  care  with  ordinary  gauges  and 
thermometers  gives  sufficient  accuracy.  For  example,  with 
IOO    pounds   absolute   boiler-pressure   and  with   atmospheric 

pressure  in  the  calorimeter,  an  error 
of  half  a  degree  by  the  thermometer, 
or  half  a  pound  by  the  boiler-gauge, 
or  a  third  of  a  pound  by  the  calo- 
rimeter-gauge will  each  give  an  error 
of  one-tenth  of  a  per  cent  in  the 
priming. 

If  steam  contains  more  than  three 
per  cent  of  priming,  the  amount  of 
moisture  can  be  determined  by  a  gooci 
separator,  which  will  remove  nearly 
all  the  moisture.  It  remains  then 
to  measure  the  steam  and  water  sep- 
arately. The  water  may  be  best 
measured  in  a  calibrated  vessel  or 
receiver,  while  the  steam  may  be 
condensed  and  weighed,  or  may  be 
gauged  by  allowing  it  to  flow  through 
an  orifice  of  known  size.  A  form 
of  this  instrument  devised  by  Professor  Carpenter*  is  shown 
by  Fig.  171. 

Steam  enters  a  space  at  the  top  which  has  sides  of  wire 
gauze  and  a  convex  cup  at  the  bottom.  The  water  is 
thrown  against  the  cup  and  finds  its  way  through  the  gauze 
into  an  inside  chamber  or  receiver,  and  rises  in  a  water-glass 
outside.  The  receiver  is  calibrated  by  trial  so  that  the 
amount  of  water  may  be  read  directly  from  a  graduated  scale. 


Fig.  171. 


*  Trans.  Am.  Soc.  Mech.  Engs.,  vol.  xvti.  p.  608. 


346  STEAM-BOILERS. 

The  steam  meanwhile  passes  into  the  outer  chamber  which 
surrounds  the  inner  receiver,  and  escapes  from  an  orifice  at 
the  bottom.  The  amount  of  steam  may  either  be  calculated, 
by  a  method  to  be  explained,  from  the  diameter  of  the  orifice 
and  the  pressure  of  the  steam,  or  it  may  be  condensed  and 
weighed  or  measured.  The  latter  is  the  more  accurate  way, 
and  it  has  the  advantage  that  then  there  is  no  error  from 
radiation,  for  the  inner  receptacle  is  well  protected  by  the 
outer  chamber,  and  condensation  in  the  outer  chamber  is 
collected  and  weighed  with  the  steam.  If  the  instrument  is 
well  wrapped  and  lagged,  and  if  a  sufficient  quantity  of  steam 
is  used,  then  the  error  from  radiation  can  be  neglected,  just 
as  was  found  to  be  the  case  with  the  throttling-calorimeter. 
This  instrument,  for  want  of  a  better  name,  is  called  a  separator 
calorimeter;  it  is  a  question  whether  either  it  or  the  throttling- 
calorimeter  are  properly  calorimeters  at  all,  and  whether  it 
would  not  be  better  to  call  both  priming-gauges. 

It  is  customary  to  take  a  sample  of  steam  for  the  calori- 
meter or  priming-gauge  through  a  small  pipe  leading  from 
the  main  steam-pipe.  The  best  method  of  securing  a  sample 
is  an  open  question;  indeed  it  is  a  question  whether  we  ever 
get  a  fair  sample.  There  is  no  question  but  that  the  com- 
position of  the  sample  is  correctly  shown  by  either  of  the 
priming-gauges  described.  It  is  probable  that  the  best  way 
is  to  take  steam  through  a  pipe  which  reaches  at  least  half- 
way across  the  main  steam-pipe,  and  which  is  closed  at  the 
end  and  drilled  full  of  small  holes.  It  is  better  to  have  the 
sampling-pipe  enter  the  steam-pipe  at  the  side  or  at  the  top  of 
the  main,  so  that  any  water  that  may  trickle  along  the  bottom 
of  the  main  shall  not  enter  the  calorimeter.  Again,  it  is  better 
to  take  a  sample  from  a  pipe  through  which  steam  flows 
upward.  The  sampling-pipe  should  be  short  and  well  wrapped 
to  avoid  radiation. 

If  the  steam  from  the  boiler  can  be  wasted  during  the  test, 
then  the  entire  steam  delivered  by  the  boiler  may  be  passed 


BOILER-TESTIXG.  i; 

through  a  large  priming-gauge,  and  the  difficulty  of  getting  a 
sample  may  be  avoided. 

Flow  of  Steam. —  It  has  been  shown  by  Rankine  *  that 
the  flow  of  steam  through  an  orifice  into  the  atmosphere  may 
be  represented  by  an  empirical  equation, 

7° 

in  which  JV  is  the  number  of  pounds  of  steam  per  second,  A 
is  the  area  of  the  orifice  in  square  inches,  and  p  is  the  absolute 
pressure  of  the  steam.  This  equation,  which  has  already 
been  mentioned  in  connection  with  safety-valves,  can  be 
applied  only  when  the  absolute  steam-pressure  is  more  than 
double  the  pressure  of  the  atmosphere;  that  is,  the  pressure 
of  the  steam  must  be  1 5  pounds  by  the  gauge,  or  more. 
Experiments  made  in  the  laboratory  of  the  Massachusetts 
Institute  of  Technology  +  show  that  this  equation  is  liable  to 
an  error  of  about  T^  per  cent,  but  this  error  may  be  deter- 
mined by  direct  experiment  for  a  given  orifice  under  various 
pressures,  and  then  a  correction  can  be  appHed  which  will 
reduce  the  error  to  a  fraction  of  one  per  cent. 

It  appears  then  that  the  use  of  an  orifice  to  determine  the 
amount  of  steam  in  Professor  Carpenter's  separator  priming- 
gauge  is  at  least  questionable  unless  direct  experiments  are 
made  to  determine  the  correction  to  be  applied.  On  the 
other  hand,  the  amount  of  steam  used  by  a  throttling  prim- 
ing-gauge may  be  very  properly  determined  by  .allowing  i4 
to  flow  through  an  orifice,  since  the  total  amount  of  steam 
used  by  the  calorimeter  is  small. 

The  same   equation   may  be  used   for  calculating  flow  of 
steam   from  one  reservoir  to  another  provided   that  the   pres 
sure  in  the  second  reservoir  is  less  than  half  that  in  the  first 


*  The  Engineer,  vol.  xxvn.  y.  359.  1869. 
f  Trans.  Soc.  Am.  Engs.,  vol.  xi.  \  .  187. 


348  STEAM-BOILERS. 

reservoir.  This  allows  us  to  gauge  small  quantities  of  steam 
used  for  any  purpose,  at  a  pressure  that  is  less  than  half  the 
boiler-pressure;  for  example,  for  running  a  steam-pump.  A 
convenient  arrangement  for  gauging  the  flow  of  steam  in  an 
inch  pipe  consists  of  a  reservoir  three  feet  long,  made  up  of 
three-inch  piping,  and  fittings  divided  at  the  middle  by  a 
brass  plate  through  which  there  is  an  orifice  of  proper  size. 
If  the  pipe  carries  steam  at  ioo  pounds  absolute,  at  a  velocity 
of  ioo  feet  a  second  it  will  deliver 

X  100  =  ^— KJ-^-  X  100  =  0.5455 

4  4 

cubic  feet  per  second.  The  density  or  weight  of  one  cubic 
foot  of  steam  at  100  pounds  absolute  is  0.2271  pounds.  So 
that  the  pipe  will  carry 

0.5455  X  0.2271  =  0.124 

of  a  pound  of  steam  per  second.  If  this  weight  is  put  for  W 
in  Rankine's  equation,  and  if  A  is  replaced  by  \  ndi,  we 
shall  have 

nd*  X  100 
0.124  = 


4  X  70 


or 


d=        /OI24. 

V     3- Hi 


24  X  4  X  70  _  1 


6  X  100         3 

of  an  inch,  nearly,  for  the  diameter  of  the  orifice  for  gauging 
the  flow  of  steam.  With  an  orifice  of  approximately  the 
right  size,  the  flow  of  steam  may  be  regulated  by  a  valve 
below  the  gauging  device;  for  example,  by  the  throttle-valve 
of  the  pump. 

Flue-gases. — At  frequent  intervals  samples  of  flue-gases 
should  be  taken  from  various  places,  such  as  back  of  the 
bridge,  from  the  uptake,  and  from  the  chimney.      These  sam- 


B01LER-TFST1NG 


349 


pies  are  analyzed  as  soon  as  may  be  by  Orsat's  apparatus,  as 
described  on  page  64. 

Though  not  commonly  done,  it  would  be  well  if  a  con- 
tinuous sample  could  be  taken  in  a  reservoir  from  which 
samples  for  analysis  could  be  taken  at  intervals. 

Draught-gauge. — The  draught  given  by  a  chimney  is 
seldom  more  than  an  inch  or  an  inch  and  a  half  of  water.  It 
can  be  measured  roughly  by  a  simple  U  tube  filled  with  water. 
An  instrument  for  accurate  determinations  of  draught  should 
be  at  once  simple  and  certain  in  its  action. 

The  draught-gauge  shown  by  Fig.   172,  devised  by  Prof. 


Fig.  172. 


Miller,  has  been  used  with  satisfaction  for  this  purpose.  It 
consists  of  two  pieces  of  three-inch  brass  pipe  connected  by  a 
half-inch  pipe  at  the  bottom.  One  of  the  pipes  is  closed  at 
he  top  and  can  be  connected  to  the  chimney  by  a  small  pipe 
with  a  valve  as  shown.  The  other  piece  of  brass  pipe  is  open 
and  has  a  hook-gauge,  reading  to  i/ioooof  an  inch,  suspended 
in  it.      In   preparing  for  a  reading,  the  closed  tube  or  leg  is 


350  STEAM-BOILERS. 

shut  off  from  the  chimney  and  opened  to  the  atmosphere;  the 
water  then  stands  at  the  same  height  aa,  a'a',  in  both  legs. 
The  closed  leg  is  now  shut  off  from  the  air  and  connection  is 
made  with  the  chimney,  whereupon  the  level  falls  to  bb  in  the 
open  leg  and  rises  to  b'b'  in  the  closed  leg.  As  the  two  legs 
have  exactly  the  same  internal  diameter,  the  fall  ab  is  half  the 
draught,  measured  in  inches  of  water.  The  hook-gauge  is  set 
to  the  level  aa  when  the  closed  leg  is  open  to  the  air,  and  to 
the  level  bb  when  it  is  connected  to  the  chimney.  The 
difference  of  the  readings  multiplied  by  2  is  the  draught  in 
inches  of  water.  The  reading  by  the  hook-gauge  can  readily 
give  an  acuracy  of  i/iooo  of  an  inch,  which  is  sufficient  for 
this  purpose. 

Pyrometers. — The  determination  of  high  temperatures, 
as  in  flues  and  chimneys,  is  difficult  and  uncertain.  Most 
commercial  pyrometers,  depending  on  the  unequal  expansion 
of  metals,  are  unreliable  if  not  misleading;  not  only  is  the 
scale  of  such  a  pyrometer  likely  to  be  incorrect,  but  the  zero 
of  the  scale  is  liable  to  change  during  use. 

The  Chatelier  pyrometer  has  been  used  with  satisfaction 
at  the  Massachusetts  Institute  of  Technology  for  measuring 
temperatures  in  flues  and  chimneys.  It  consists  essentially 
of  a  thermoelectric  couple  made  by  joining  the  ends  of  two 
wires,  one  of  platinum  and  the  other  of  platinum  alloyed  with 
ten  per  cent  of  rhodium.  All  but  about  four  inches  of  the  wire 
at  the  junction  is  incased  in  fire-clay  inside  an  iron  pipe 
about  four  feet  long.  From  the  wires  of  the  pyrometer  con- 
nection is  made  to  a  sensitive  galvanometer  in  a  separate 
observing-room.  The  deflection  of  the  galvanometer  is  indi- 
cated by  a  ray  of  light  reflected  from  a  mirror  on  the  needle 
and  moving  over  a  graduated  scale.  The  scale  is  set  to  read 
zero  when  the  junction  of  the  wires  is  at  the  temperature  of 
the  atmosphere.  The  junction  is  then  immersed  successively 
in  baths  of  substances  which  melt  at  various  high  tempera- 
tures, such  as  sulphur  and  naphthaline.     The  readings  of  the 


BOILER-TESTING.  35 1 

ray  of  light  when  the  juncture  is  in  such  baths  fix  known 
points  on  the  arbitrary  scale  from  which  intermediate  tem- 
peratures may  be  estimated  directly.  It  is  convenient  to  use 
a  curve  for  this  purpose  with  scale-readings  for  abscissae  and 
with  corresponding  temperatures  for  ordinates.  After  the 
scale  is  determined  the  pyrometer  may  be  introduced  into  the 
place  or  places  where  temperatures  are  to  be  measured,  and 
readings  are  taken  from  which  the  temperatures  are  deter- 
mined by  interpolation  on  the  curve  just  described. 

Air-supply. — The  air  for  a  furnace  may  be  made  to  enter 
through  a  temporary  mouthpiece  fitted  to  the  ash-pit  doors. 
This  mouthpiece  may  be  of  galvanized  iron,  circular  in  sec- 
tion and  about  three  feet  long.  Its  cross-section  should  have 
an  area  equal  to  that  of  the  door  or  doors  leading  to  the  ash- 
pit. The  velocity  of  the  air  passing  through  the  mouthpiece 
can  be  measured  by  an  anemometer.  The  area  of  the  mouth- 
piece multiplied  by  the  velocity  in  feet  per  second  gives  the 
volume  of  air  supplied  to  the  ash-pit  in  cubic  feet  per  second. 
From  this  may  be  calculated  the  volume  and  weight  of  air 
supplied  to  the  ash-pit  per  hour  or  for  the  entire  test;  which 
weight  divided  by  the  total  coal  consumption  gives  the  air 
per  pound  of  coal  burned. 

It  should  be  noted  that  the  anemometer  is  liable  to  an 
error  of  from  two  to  five  per  cent,  and  further  that  air  enter- 
ing through  the  fire-doors  and  elsewhere  than  through  the  ash- 
pit is  not  measured. 

Sample  Test. — The  test  given  on  page  352,  made  at  the 
Massachusetts  Institute  of  Technology,  may  serve  as  an 
example  of  a  convenient  arrangement  for  reporting  the  data 
and  results  of  a  boiler-test. 

The  average  pressure  of  the  air  and  of  the  steam  in  the 
boiler  are  liable  to  vary  slightly  during  the  test;  the  average 
pressures  were  obtained  from  readings  taken  at  regular  inter- 
vals during  the  test.  The  same  may  be  said  of  the  tempera- 
ture of  the  feed-water. 


352 


STEAM-BOILERS. 


EVAPORATIVE    TEST    ON    BOILER    PLANT. 

Date.  /'^-J'o.  >QO'.  4  P.M.,  to  fan.  4,1002.  SA.M. 


DATA. 
Brief  description  of  method  of  testing  : 

The  feed-water  was  weighed  and  delivered  to  a  barrel  connected  to  the  suction  of  the  feed- 
pump 

Coal  was  weighed  in  joo  lb.  lots  as  fired. 

Calorimeter  readings  were  taken  every  hour. 

Flue-gas  samples  every  half  hour ;  all  other  readings  quarter  hours. 

Fires  were  cleaned  two  hours  before  starting  and  same  time  before  the  ending  and  twice 
during  twenty-four  hours. 

Blozu-of  pipes  were  blanked. 
Brief  description  of  boilers: 

Boilers  No.  4  and  No.  5,  horizontal  multitubular,  lb'  long. 

Diameter  of  shell  =  bo"  ;     S4  3"  tubes  lb'  long. 

Grates  bc%"  X  bi%"  {Herringbone  grates). 

Boilers  No.  b  and  No.  7  are  furnished  with    Hawley  down-draught  furnaces ;  otherwise 
they  are  the  same  as  Boilers  No.  4  and  No.  5. 


Duration  of  test 

Barometer      .... 

Boiler  pressure  (gauge) 

Temperature  of  the  air 

Temperature  of  feed  water 

Temperature  of  steam 

Degrees  of  superheat 

Quality  of  steam,  dry  steam  unity 

Kind  of  coal  used    . 

Moisture  in  coal,  by  drying  test 

Total  water  fed  to  boilers 


Type  of  Boiler  and  Number  of 
Boiler. 


Horizontal  multitubular  N0.4. 

No.  5. 

No.  b. 

"  "  No.  7. 


113    hours. 
20.ob  inches,  T4-7Q  pnnnHs, 

'°°-°     ponnHs 

inside     0!  '"     F.;   outside    2°-°°     F. 


*-f-4°     C, 

°  c, 

o    C, 


75-0° 


■QQl 

New  River. 

'•3    per  cent. 
746, 4S7  pounds. 


e  o 


OS 


•=  so 

XX2 


25.Q    1  42-06-1 


1,113 


25 -Q 


/,/bb 


1. /Ob 


42.06-1 


57-45' 


22. 1  So 


2O.OQ0 


1 8. 073 


U  a 

r*3 


tr.  — 


23.OO6 


21.S02 


10.820 


rS.72b 


1.815 


2.Q55 
2.003 


6  u 


2 1.b47 


20,077 

H-774 


16,723 


4,358       Q2.4       40-35-1    84,643  I   83.544  j    7.322       76,222 


Total  ash  and  clinker  in  per  cent,  total  dry  coal 


S.76 


BOILER  TESTING. 
EVAPORATIVE   TEST   ON    BOILER    PLANT. 


353 


Chemical  analysis  of  coal  "« 


H-O  =  o.r. 


RESULTS. 
C  =  qo.o,     H  =  o.j, 


O  = 


Heat  of  combustion  of  coal  as  fired  ..... 

Total  equivalent  evaporation  from  and  at  2i2°  F. 
Equivalent  evaporation  from  and  at  2120  F.  per  pound  of  dry  coal    . 
Equivalent  evaporation  from  and  at  2120  F.  per  pound  of  combustible 
Equivalent  evaporation  from  and  at  2120  F.  per   square  foot  of   heating 

surface  per  hour.  .... 

Coal  burned  per  square  foot  of  grate  surface  per  hour 
Boiler  horse-power  developed,  A.  S.  M.  E.  rating 
Maximum  assumed  possible  error  of  test  . 
Air  per  pound  of  coal  from  analysis  of  flue  gases 

Air  required  per  pound  of  coal  from  the  formula  I  12  C  -f-  36  (  H ;r) 

Excess  air  supplied     ..... 
Heat  carried  off  by  flue  gases  per  pound  of  coal 
Heat  taken  up  by  water  in  boiler  per  pound  of  coal 
Total  heat  furnished  per  pound  of  coal 
Heat  radiated  per  pound  of  coal     . 
Heat  carried  off  by  flue  gases 
Thermal  efficiency  of  boiler  plant  . 
Heat  lost  by  radiation,  etc.  . 


1.7,    Ash  =  7.5. 
'4,555  B  T.U. 
875T70  pounds 

IQ-4S  pounds 
"•49  poun,i% 


JllZfLpcunds. 
8.18  , 


.pounds. 


226 . 5 
0  &7  per  cent. 


3° -7  pounds. 
10. 0  pounds. 
'°2  per  cent. 


Wfr  B  T.U. 


10,033  B.T.U. 

14,555  B.T.U. 

2.017  B.T.U. 

17 .  1  per  cent. 

6S.0  per  cent. 

i_4.o  per  cent. 


GAS   ANALYSIS  :    Per  cent  by  volume. 


CO, 

oa 

CO 

Bet.  bridge  wall 

coa 

o2 

CO 

and  back  end 

Above  grate    . 

Back  end    . 

At  bridge  wall 

Uptake 

6.4 

I2.Q 

O.I 

DRAUGHT   AND    TEMPERATURES. 


Setting. 

Inches  of 
Water. 

°F. 

Stack. 

Inches  of 
Water. 

•F. 

Ash-pit 

Above  grats 

At  bridge  wall 

Between  bridge  wall  and 

.02 

feet  above  grate. 

.07 

.00 

Back  end     . 
Uptake 

•  04 
.07 

30' 

«         „          .. 

Remarks: 

The  coal  was  of  poor  quality.     Fires  were  hard  to  clean,  as  there  were  bad  clinkers. 

The  firing  was  good. 


354  STEAM-BOILERS. 

Total  equivalent  evaporation  from  and  at  2120  F.: 

(.991^+9)  at  absolute  ^boiler-pressure  is 1181.7  B.T.U. 

(q)  at  temperature  of  feed-water  (75. 90  F.)  is 44.0 

Heat    necessary  to  vaporize  a  pound   of  feed-water 

into  steam  primed  .9  per  cent  is 1137. 7  B. T. U. 

H37-7  X  74'6457      o 

— J/      '    ' £1  =  875770  pounds. 

969.7 

969.7  is  the  latent  heat  of  steam  at  2120  F. 


Equivalent  evaporation  from  and  at  212°  F..per  pound  0/  dry  coal  : 
875770 


S3544 


10.48  pounds. 


Equivalent   evaporation  from    a?id  at  212°  F.  per  pound  of  dry 
combustible  : 

87577°  , 

— -=- =  11.40  pounds. 

76222 


Equivalent   evaporation  from    and  at  2i2J   F.  per  square  foot  of 
heating  surface  per  hour : 

s7577°  a 

=  1.72  pounds. 


4558  X  112 


Coal  burned  per  square  foot  of  grate  surface  per  hotir  „• 

-J^4A_  =  .8.18  pounds. 

92.4  X  112 


BOILER-TESTIXG 


OOO 


Boiler  horse- pouer  developed  (A.S.M.E.  rating).    (See  page  148.) 

H37-7  X  746457       ,    r  . 
—  220.3 

112  x  33+70 


Maximum  assumed  possible  error  of  test. — It  is  assumed  that  an 
error  of  one  inch  may  oe  made  in  estimating  the  thickness  of  each 
fire  at  the  beginning  and  at  the  end  of  the  test  and  that  these  errors 
ave  cumulative,  thus  making  the  total  error  two  inches  over  the  entire 
grate.     For  soft  coal  the  weight  of  a  cubic  foot  is  about  48  pounds. 

92.4  X  48  x  T-o  =  739-2  pounds  error. 
739.2  X  100 


84643 


=  0.07  per  cent. 


Thermal  efficiency  of  boiler  plant. — This  is  the  ratio  of  the  heat 
taken  up  by  the  water  in  the  boilers  per  pound  of  coal  fired  to  the 
heat  given  up  by  a  pound  of  coal  as  fired. 

ii37-7X746457Xioo 

jr— 2 =  6b. 9  per  cent. 

14555  X  «4^+3  yi 


Air  per  pound  of  coal  from   analysis  of  flue- gases.      (Se*  pages- 
67-68-69.) 

C02  =    6.4x22=:  140.8;  T\  x  140.8  =  38.4  c 

02  =  12.9  X  16  =  206.9 

CO—    o-.iXi4=       1.4;  tX       1.4=    0.6  C 

348.6  39.0  C 

348.6  -  39  =  309.6  0.. 


350  STEAM-BOILERS 

309.6 


39 

7-94 
.232 


=  7.94  pounds  of  oxygen  per  pound  of  carbon. 
=  34.2  pounds  of  air  per  pound  of  carbon. 


As  the  coal  is  90  per  cent  carbon,  the  air  per  pound  of  coal  is 
30.8  pounds. 


Air  required  per  pound  of  coal  from  formula  : 
i2C+36^H---J      =  I  12  X  .9  +  36^oo5  +  ,-^p-\j  =  io.9  pounds. 


Excess  of  air  supplied: 

(30.8  —  10.9)100 
10.9 


=  182  per  cent. 


Heat  carried  off  by  the  gases  per  pound  of  coal. — -There  were  30.8 
pounds  of  air  and  .9  pounds  of  carbon,  making  31.7  pounds  of  gas  for 
each  pound  of  coal  burned. 

The  proportion  of  the  gases  by  weight  may  be  figured  from  the 
flue-gas  analysis: 

C02        6.4  X  22  -     140.8 

02     12.9  X  16  =    206.9 

CO        0.1  X  14  =         1.4 

N2     80.6  X  14  =  1128.4 

100. o  1477-5 

4°'      X  31.7  =     3-°2>  tne  weight  of  CO 
U77-5 

—  X  ^i-7  =     4-44,  the  weight  of  O, 

1477-5  ' 

X  31.7  =     0.03,  the  weight  of  CO 


1477-5 

—  x  ^?i.7  =  ^4.21,  the  weight  of  N 

U77-5 


BOILER-TESTIXC. 


357 


The  temperature  of  the  flue  was  3910  F.,  while  the  air  in  the  boiler- 
room  was  6i°  F.;  a  difference  of  3300  F. 

Multiplying  the  weights  of  the  gases  by  their  specific  heats  and  by 
the  number  of  degrees  increase  in  temperature.     (See  pages  55-72.) 

Weight.  SPC(iflc         Temperature 

0  Heat.  Increase. 

C02 3.02  .2169  330  216.2 

02 4-44  .2175  330  318.6 

CO 03  .2450  330  2.4 

N2 24.21  .2438  330  JQ47-8 

2485.0 

No  allowance  has  been  made  for  the  moisture  in  the  coal  or  for 
the  moisture  in  the  air.  This  moisture  might  amount  to  90  or  95 
heat-units  in  a  total  of  2500. 

A  much  simpler  method  of  finding  the  heat  carried  off  by  the  flue- 
gases,  although  not  as  accurate  as  the  one  given  above,  is  sufficientlv 
accurate  for  most  work. 

There  are  31.7  pounds  of  gas  per  pound  of  coal;  call  the  average 
specific  heat  of  flue-gas  .235.     The  heat  carried  away  is  then 

31. 7X330X. 235  =  2474, 

which  varies  from  2485  by  but  11  heat-units. 

Heat  taken  up  by  the  u-ater  in  the  boiler  per  pound  of  coal  as  fired: 

1137^X^46457  =u 

84643 

Heat  radiated  per  pound  of  coal: 

14555  —  10033  —  2485  =  2037  B.T.U. 

Heat  carried  off  by  flue  gases: 

2485  X  100 

—=17.1  per  cent. 

14555 

Heat  lost  by  radiation: 

2037  X  100 

-  =  14. 1 1  per  cent. 
14555 


358  STEAM-BOILERS. 

Heat  Balance. — The  heat  given  up  by  the  coal  is  accounted 
for  as  heat  put  into  making  steam,  as  heat  carried  off  by  the 
flue-gases,  and  as  heat  radiated  from  the  setting  to  the  air. 

The  heat  taken  up  in  making  steam  and  that  carried  off  by 
the  flue-gas  may  be  calculated  from  the  data  obtained  during  the 
test,  but  the  heat  lost  by  radiation  can  only  be  found  by  subtract- 
ing the  sum  of  the  preceding  from  ioo.  This  should  be  from 
8  to  15  per  cent,  depending  on  how  hard  the  boiler  is  being  forced, 
and  on  the  amount  and  thickness  of  the  brickwork. 

A  Scotch  boiler  will  show  only  2  to  4  per  cent  loss  by  such 
radiation. 

Should  the  radiation  come  out  negative  it  shows  inaccuracy 
in  the  test.  This  inaccuracy  may  be  due  to  errors  in  weighing 
coal  or  to  the  conditions  at  the  start  and  at  the  end  not  being  the 
same.  At  times,  even  though  an  engineer  does  his  best  to  con- 
duct a  test  fairly,  he  may  be  cheated  by  the  fireman. 

It  is  not  out  of  place  to  point  out  here  some  of  the  ways  by 
which  an  unfair  result  may  be  obtained  by  an  honest  engineer. 

1.  By  forcing  the  boiler  abnormally  for  two  or  three  hours 
before  the  test  begins,  thus  storing  up  heat  in  the  brickwork 
which  is  given  out  later  when  the  boiler  is  under  test.  This  may 
be  obviated  by  keeping  the  boiler  at  its  test  rating  for  two  hours 
before  starting  the  test. 

2.  If  a  boiler  is  working  hard  the  water-level  is  lifted  more 
than  when  the  boiler  is  steaming  easily.  By  crowding  the  boiler 
for  a  few  minutes  just  as  the  test  begins  and  by  checking  the 
boiler  at  the  end  of  the  test  the  indication  by  the  glass  may  be 
made  to  vary  one  inch  with  the  same  amount  of  water  in  the  boiler 
at  the  start  and  at  the  finish. 

As  the  level  in  the  boiler  is  judged  by  the  height  in  the  glass, 
too  much  water  would  be  put  into  the  boiler  near  the  end  of  the 
test  when  the  rate  of  evaporation  decreased.  If  the  boiler  is 
kept  working  at  the  same  rate  and  at  the  same  pressure  through- 
out the  test,  the  error  from  this  source  would  be  avoided. 

3.  In  many  vertical  boilers  the  water  connection  of  the  com- 


BOrLER-TESTING.  359 

bination  carrying  the  gauge  glass  comes  from  the  shell  just  above 
the  crown-sheet. 

This  makes  a  column  of  water  outside  the  boiler  perhaps 
10  feet  in  height.  This  column  is  balanced  by  the  water  inside 
the  boiler.  Just  before  beginning  the  test  the  fireman  will  blow 
out  the  combination  (to  satisfy  you  that  it  is  working  freely). 
The  piping  and  glass  now  fill  with  hot  water,  and  the  level  in  the 
boiler  and  the  level  in  the  glass  are  the  same.  As  there  is  no 
circulation  in  the  pipe  leading  to  the  water  end  of  the  combina- 
tion, the  water  gradually  cools  and  a  column  of  cold,  or  com- 
paratively cold,  water  is  balancing  a  column  of  hot  water  in  the 
boiler. 

If  the  level  in  the  glass  is  made  the  same  at  the  end  of  the 
test  as  at  the  beginning,  the  level  in  the  boiler  will  be  from  6 
to  10  inches  higher  than  at  the  beginning.  By  having  the  com- 
bination blown  just  before  the  end  of  the  test  this  error  is  avoided. 

4.  Sometimes  plans  to  cheat  the  engineer  are  deliberately 
made.  The  engineer  may  insist  that  the  blow-off  pipe  and  all 
feed-pipes,  excepting  those  from  his  weighing-tanks,  be  blanked, 
and  yet  he  may  get  an  impossible  evaporation. 

A  small  pipe  1/4  inch  in  diameter  starting  below  the  water- 
line  may  lead  up  inside  of  the  steam-pipe  and  run  perhaps  100 
feet,  where  it  appears  on  the  outside  of  the  pipe  as  a  drip-pipe 
for  removing  condensation  from  the  pipe.  It  is  evident  that  if 
this  "drip-valve"  is  manipulated  most  any  evaporation  could 
apparently  be  obtained. 

If  an  engineer  has  any  doubts  about  the  honesty  of  the  parties 
concerned  he  may  protect  himself  against  any  cheating  similar 
to  that  referred  to  above  by  cutting  the  boiler  under  test  from  the 
steam-main  and  by  blowing  all  the  steam  generated  into  the  air 
through  an  orifice  of  known  area. 

The  weight  of  steam  (figured  by  Rankine's  or  Napier's  for- 
mula) flowing  through  the  orifice  plus  the  steam  used  in  the 
calorimeter  plus  the  steam  used  by  the  feed-pump  should  equal 
the  feed-water  weighed. 


CHAPTER   XII. 
BOILER    DESIGN. 

In  order  to  bring  together  the  principles  and  methods 
which  have  been  given  in  the  preceding  chapters,  they  will  be 
applied  to  the  design  of  a  boiler.  Designing  of  any  sort  is  an 
art  that  is  guided  and  controlled  by  practical  considerations 
and  theoretical  principles,  and  which  can  be  acquired  by  prac- 
tice only.  The  design  of  a  boiler,  like  many  other  designs, 
is  further  modified  to  meet  the  requirements  of  government 
boards  of  inspection,  or  to  conform  to  the  inspection-rules  of 
insurance  companies.  These  rules  and  requirements  vary 
from  place  to  place  and  from  time  to  time;  they  must  be 
known  to  the  designer,  but  they  have  no  place  in  a  text-book. 
A  simple  and  common  type  of  boiler  has  been  chosen  for 
design;  the  methods,  with  proper  modification,  can  be  applied 
to  other  types,  and  the  general  principles  illustrated  are  much 
the  same  for  all  types. 

Type  of  Boiler. — The  kind  of  boiler  used  in  a  given 
locality  depends  on  custom,  on  the  kind  of  water  used,  and  on 
the  cost  and  quality  of  fuel.  Deviation  from  common  prac- 
tice should  be  made  only  for  sufficient  reason.  Where  water 
is  bad  or  where  fuel  is  cheap,  the  plain  cylindrical  boiler  or  a 
flue-boiler  will  be  chosen.  With  clean,  soft  water  the  cylin- 
drical tubular  boiler,  like  that  shown  by  Plate  I,  has  been 
found  to  be  convenient,  economical,  and  cheap.  All  these 
boilers  have  external  furnaces,  so  that  the  shell  is  in  part 
exposed  to  the  fire.  Now  plates  exposed  directly  to  the  fire 
should  not  be  more  than  half  an  inch  thick;  3/8  of  an  inch  is 
preferable.      Though  thicker  plates  are  sometimes  used,  this 

360 


BOILER    DESIGN.  36 1 

consideration  limits  the  size  of  boilers  of  this  type  when  high 
pressures  are  used.  The  importance  of  high  efficiency  for  the 
longitudinal  riveted  joint  becomes  apparent  in  this  connec- 
tion. 

Internally-fired  boilers,  like  the  Lancashire  or  the  Scotch 
marine  boiler,  are  not  limited  in  diameter  by  this  reason. 
The  marine  boiler  sometimes  has  plates  an  inch  and  a  quarter 
thick;  the  fact  that  so  great  a  thickness  is  undesirable  some- 
times serves  as  a  check  on  the  size  of  such  boilers. 

General  Proportions. — Whatever  may  be  the  type  of 
boiler  chosen,  there  must  be  provided — 

1.  Sufficient  grate-area  to  burn  the  fuel  required  under  the 
available  draught. 

2.  Suitable  combustion-space  to  properly  burn  the  fuel. 

3.  Sufficient  area  ot  flues  or  tubes  to  carry  off  the  products 
of  combustion. 

4.  Sufficient  heating-surface  to  absorb  the  heat  generated. 

5.  Proper  water-space  to  prevent  too  great  a  fluctuation 
of  the  water-level  when  there  is  an  irregular  demand  for  steam. 

6.  Suitable  steam-space  to  prevent  too  great  a  fluctuation 
ot  pressure  when  steam  is  taken  at  intervals,  as  for  the  cyl- 
inder of  a  steam-engine. 

7.  Sufficient  free-water  area  for  disengagement  of  steam. 

The  last  three  conditions  are  not  fulfilled  by  most  water- 
tube  boilers;  some  such  boilers  depend  on  a  separator  for 
disengaging  steam  from  water. 

Problem  for  Design. — Let  it  be  required  to  determine 
the  main  dimensions  and  some  of  the  details  of  a  hori- 
zontal cylindrical  tubular  boiler  to  develop  80-horse  power 
A.  S.  M.  E.  standard  (page  148).  Let  the  working-pressure 
be  150  pounds  per  square  inch  by  the  gauge,  and  the  test- 
pressure  225  pounds,  or  once  and  a  half  the  working-pressure. 

Assume  that  anthracite  coal  will  be  used,  and  that  it  will 
give  an  equivalent  evaporation  of  9  pounds  of  water  per 
pound  of  coal  from  and  at  2120  F.     Assume    further  that  12 


362  STEAM-BOILERS. 

pounds  of  coal  will  be  burned  per  square  foot  of  grate-surface 
per  hour. 

The  heating-surface  may  be  about  thirty-seven  times  the 
grate-surface.  Tubes  16  feet  long  will  be  used,  which  length 
should  not  much  exceed  sixty  times  the  diameter. 

The  area  through  the  tubes  will  be  made  about  1/7.5  °f 
the  grate-area. 

Grate  -  area. — The  A.  S.  M.  E.  standard  requires  that 
34.5  pounds  of  water  per  hour  shall  be  evaporated  from  and 
at  2120  F.  for  each  horse  -  power.  The  total  equivalent 
evaporation  will  consequently  be 

80  X  34.5  =  2760  pounds  per  hour. 

With  an  equivalent  evaporation  of  9  pounds  of  water  per 
pound  of  coal  the  coal  burned  will  be 

2760  -v-  9  =  307  pounds  per  hour. 

With  a  rate  of  combustion  of  12  pounds  of  coal  per  square 
foot  of  grate  surface  per  hour,  the  grate-area  must  be 

307  -H  12  =25.6  square  feet. 

Tubes. — A  common  rule  for  finding  the  diameter  of 
tubes  is  to  allow  one  inch  for  each  four  feet  of  length  when 
soft  coal  is  used,  and  five  feet  when  hard  coal  is  used.  A 
tube  three  inches  in  diameter  will  very  nearly  fulfil  this 
condition. 

The  table  of  proportions  of  flue-tubes  in  the  Appendix, 
gives  the  area  of  the  internal  transverse  section  of  such  a  tube 
as  6.08  square  inches;  the  external  area  is  7.07  square  inches. 
The  internal  circumference  is  8.74  inches,  and  the  external 
curvmference  is  9.42  inches. 


BOILER    DESIGN.  363 

The  aiea  through  the  tubes  has  been  chosen  as  1/7 
the  grate-area,  equal  to 

25.6  X    144  „  .     . 

-  =  402  square  inches. 

7.5 

Since  the  area  through  one  tube  is  6.08  square  inches, 
there  will  be  required 

492  ^6.08  =  80.8, 

or,  more  properly,  81  tubes.  It  may  be  found  convenient  in 
laying  out  the  tube-sheet  to  use  more  than  this  number  of 
tubes;  a  less  number  is  of  course  improper. 

Steam-space. — A  good  rule  for  this  type  of  boiler  is  to 
allow  from  0.8  to  1  cubic  foot  of  steam-space  per  horse- 
power, which  gives  from  64  to  80  cubic  feet  for  this  boiler. 
We  will  assume  80  cubic  feet. 

For  sake  of  comparison,  calculations  will  be  made  also  by 
rules  given  on  page  132.  Thus  for  certain  boilers  working  at 
moderate  pressures  it  is  found  that  the  steam-space  may  be 
made  equal  to  the  volume  of  steam  used  by  the  engine  in  20 
seconds.  Suppose  that  this  boiler,  though  designed  for  150 
pounds  pressure,  may  run  at  70  pounds  pressure,  and  may 
supply  an  80  horse-power  engine  which  uses  30  pounds  of 
steam  per  horse-power  per  hour. 

Now  the  volume  of  one  pound  of  steam  at  70  pounds  by 
the    gauge,   or   85   pounds    absolute,   is    5.16  cubic    feet, 
that  the  engine  will  use 

80X30X5.16=12.384 

cubic  feet  of  steam  in  an  hour,  or 

20 

X  12384  =  68 


600 


o 


cubic  feet  in  20  seconds.       This   is   about  the   lower  limit  by 
the  rule  used  above.     It  is  clear  that  the  steam-space  would 


364  STEAM-BOILERS. 

be  very  small  if  determined  by  this  rule  for  an  engine  using 
steam  at  150  pounds  pressure. 

Another  rule  makes  the  steam-space  from  50  to  140  times 
the  volume  of  the  high-pressure  cylinder  of  the  engine;  50 
for  very  high  pressure  and  high  speed,  140  for  slow  speed 
and  low  pressure.  For  medium  speeds  and  pressures  60  to 
90  may  be  used. 

The  boiler  under  consideration  may  supply  steam  to  a 
triple-expansion  engine  which  has  a  high-pressure  cylinder  9 
inches  in  diameter  by  30  inches  stroke,  so  that  the  volume  is 
1. 105  cubic  feet.  According  to  this  the  steam-space  needed 
is  66  to  99  cubic  feet. 

Diameter  of  Boiler. — For  this  type  of  boiler  the  steam- 
space  is  commonly  made  one  third  and  the  water-space  two 
thirds  of  the  contents  of  the  boiler.  To  the  contents  of  the 
boiler  there  must  be  added  the  space  occupied  by  the  tubes  to 
find  the  volume  of  the  cylindrical  shell.  Now  we  have  de- 
cided to  use  81  tubes  3  inches  in  diameter  and  16  feet  long. 
The  area  of  the  external  transverse  section  has  been  found  to 
be  7.07  square  inches.  The  space  occupied  by  the  tuoes  is 
consequently 

81  X  7-Q7X    16  =     64cubicfeet. 
144 

To  this  add  steam-space,  80      " 

and  water  space,  160     " 


Making  in  all,  304     " 

The  cylinder  is  16  feet  long,  so  that  its  transverse  area  is 

304  -r-  16  =  19  square  feet; 

which  corresponds  to  a  diameter  of  59.02  inches,  or  nearly  60 
inches.  This  will  be  taken  as  the  trial  diameter;  it  may  re- 
quire change  in  proportioning  other  parts  of  the  boiler. 

The   method   of   determining   the    main  dimensions    of    a 


BOILER    DESIGN.  365 

boiler  from  the  steam-space  will  require  modification  if  it  is 
applied  to  any  other  type  of  boiler.  Even  when  applied  to 
a  given  type  it  leaves  much  to  the  judgment  of  the  designer, 
who  may  find  difficulty  in  using  it  unless  he  is  accustomed  to 
working  on  that  particular  type.  If  the  designer  has  at  hand 
the  dimension  of  several  boilers  of  a  given  type,  he  may  pre- 
fer to  select  the  main  dimensions  for  a  new  design  directly, 
with  the  reservation  that  such  dimensions  may  be  modified 
as  the  design  proceeds.  This  is  commonly  done  by  the 
designers  of  marine  and  locomotive  boilers. 

Heating-surface. — The  heating-surface  of  a  cylindrical 
tubular  boiler  consists  of  all  the  shell  below  the  supports  at 
the  side  wall,  all  the  inside  of  the  tubes,  and  part  of  the  rear 
tube-plate.  Usually  half  of  the  cylindrical  part  of  the  shell 
is  heating-surface.  •  In  the  case  in  hand  the  heating-surface, 
exclusive  of  the  tube-plate,   will  amount  to 

C1    11  l  .,  3-HI6  X  60  X  16 

Shell -X  =  125.7  sq.  ft. 

8.74  X  16 
Tubes....     81  X  — — =  943.9   "    " 


Total 1069.6   "     " 

The  grate-surface  is  to  be  25.6  square  feet,  so  that  the 
ratfo  of  grate-surface  to  heating-surface  will  be  at  least  as  good 
as 

25.6  :  1069.6  ::  1   :  41^. 

The  actual  ratio  will  be  more  favorable  as  it  will  appear 
advisable  to  use  more  than  81  tubes,  and  the  back  tube-sheet 
remains  to  be  allowed  for. 

Water-level. — It  is  now  necessary  to  determine  the  posi- 
tion of  the  water-level  to  see  if  there  will  be  sufficient  free- 
water  surface  and  sufficient  distance  from  the  water-level  tc 
the  shell  above  it. 


366  STEAM-BOILERS. 

Since  the  whole  boiler  is  cylindrical,  the  area  of  the  head 
of  the  boiler  exposed  to  steam  and  to  water  will  have  the 
same  ratio  as  that  of  the  steam-space  to  the  water-space. 
Consequently  the  area  of  the  head  above  the  water-level  must 
be  one  third  of  the  total  area  of  the  head  less  the  combined 
areas  of  the  tubes. 

The  area  of  a  circle  having  a  diameter  of  60  inches  is 
2827.4  square  inches.  The  area  of  81  tubes  each  having  an 
external  cross-section  of  7.07  square  inches  will  be 

81  x  7-07  =  572.7 

square  inches.  The  area  of  the  head  exposed  to  steam  is 
consequently 

2827.4-  572.7  _  6 

3 

square  inches.  We  need  now  to  know  the  height  of  a  seg- 
ment of  a  60-inch  circle,  which  has  the  area  of  75 1.6  square 
inches.  The  second  problem  in  the  explanation  of  the  use  of 
a  table  of  segments  (see  Appendix)  gives  for  the  tabular 
number  corresponding  to  the  area 

751.6 
2^ — 2-  =  0.2088; 
60  X  60 

for  which  the  ratio  of  the  height  to  the  diameter  is  0.312, 
The  height  of  the  segment  is  therefore 

0.312  X  60  =  18.7  inches. 

This  gives  sufficient  height  above  the  water,  and  sufficient 
free-water  surface.     The  water-level  will  be 

30—  18.7  =  n. 3 

inches  above  the  centre  of  the  boiler. 

Factor  of  Safety. — It  has  been  pointed  out  that  the  actual 
factor  of  safety  of  boiler-shells  is  usually  four  or  five  when  the 
boiler  is  built.     The  apparent  factor  of  safety  for  some  parts 


BOILER     DESIGN.  367 

like  stay-bolts  may  be  greater,  but  such  factors  are  illusory 
because  the  stays  may  be  subjected  to  considerable  irregular 
stress  from  unequal  expansion.  The  apparent  stress  on  stay- 
rods  and  bolts,  from  steam-pressure  only,  is  frequently  limited 
by  inspection-rules  or  by  law. 

The  factor  of  safety  of  a  boiler  which  has  been  at  work 
for  some  years  is  much  affected  by  corrosion,  which  acts  upon 
different  parts  of  the  boiler  very  differently,  even  when  the 
corrosion  is  uniform.  Thus  a  plate  half  an  inch  thick  will 
have  7/8  of  its  original  strength  after  it  has  lost  1/16  of  an 
inch  by  corrosion.  The  weakest  part  of  the  plate,  that  is, 
the  riveted  joint,  seldom  suffers  as  much  from  corrosion  as  the 
whole  plate  at  a  distance  from  the  joint,  because  the  plate  is 
protected  to  some  extent  by  the  rivet-heads.  Some  forms  of 
joint  have  an  internal  cover-plate,  which  protects  the  plate  at 
the  joint  and  the  joint  may  be  nearly  as  strong  after  corrosion 
as  before.  Very  often  old  weak  boilers  fail  by  tearing  the 
corroded  plate  outside  the  riveted  joint. 

Stay-rods  and  bolts  suffer  much  more  from  corrosion  than 
plates.  Thus  a  rod  one  inch  in  diameter  has  an  area  of 
O.7854  of  a  square  inch.  After  corrosion  to  the  extent  of 
1/16  of  an  inch  has  taken  place  the  diameter  is  7/8  of  an 
inch  and  the  area  is  0.6013,  which  is 

0.6013  -*-  °-/S54  =  0.766 

ot  the  original  area.  Compare  this  with  the  plate  which 
retains  7/8  or  0.875  of  its  thickness  after  the  same  amount  of 
corrosion.  Of  course  a  smaller  stay  will  suffer  more,  and  a 
larger  one  less,  in  proportion. 

After  the  sizes  of  the  parts  of  a  boiler  are  decided  upon  it 
is  well  to  make  calculation  to  see  that  a  factor  of  safety  of 
four  will  remain  after  a  reasonable  amount  of  corrosion.  Or, 
as  in  the  case  of  stay-rods,  the  size  may  be  calculated  with  a 
proper  factor,  and  then  the  diameter  may  be  increased  to 
allow  for  corrosion. 


368 


STEAM-BOILERS. 


Thickness  of  Shell. — The  final  decision  of  the  proper 
thickness  of  the  shell  for  the  boiler  under  consideration  can- 
not be  made  until  the  efficiency  of  the  joint  is  known;  but 
the  efficiency  of  any  of  the  complex  joints  now  in  vogue  can 
be  found  only  when  the  thickness  of  the  plate  is  known.  It 
is  therefore  convenient  to  assume  a  factor  of  safety  of  about  six 
and  make  a  preliminary  calculation. 

Thus  for  the  boiler  in  hand  we  will  get  for  the  thickness 
(page  184) 

150  X  30 
t  —      3  ^  ,  =  0.49 

55,000  -h  6 

of  an  inch.     A  similar  calculation  with  a  factor  of  five  gives 

1 50  X  ^o 

=  0.4? 


55,000-^  5 

of  an  inch.  The  shell  will  be  either  7/16  or  1/2  an  inch 
thick.  Seven  sixteenths  will  give  an  apparent  factor'  of 
safety  of 

55,000  X  7/16  =  - 
150  X  3° 

After  the  allowance  for  the  efficiency  of  the  joint  has  been 
made  this  factor  will  be  found  to  be  about  4f . 

Longitudinal  Joint. — The  shell-plate  is  made  as  thin  as 
possible  because  it  will  be  exposed  to  the  fire.  Consequently 
the  efficiency  of  the  longitudinal  riveted  joint  must  be  high  if 
the  real  factor  of  safety  is  to  be  satisfactory.  The  strength 
of  triple-riveted  joints  like  that  shown  on  page  214  ranges 
from  85  to  90  per  cent.  The  joint  with  two  cover-plates 
shown  by  Fig.  173,  will  be  chosen.  Following  the  method 
given  on  page  214,  it  appears  that  this  joint  may  fail  in  one 
of  five  ways,  for  which  the  resistances  are  as  follows: 

A.  Tearing  at  outer  row  of  rivets: 

Resistance  =  (P  —  d)tft. 


BOILER  DESIGN. 


3^9 


B.  Shearing  four  rivets  in   double  shear  and  one  in    single 

shear : 

qnd'1 

Resistance  = fs. 

4 

C.  Tearing  at  the  middle  row  of  rivets  and  shearing  one  rivet: 

nd* 
Resistance  =  (P  —  2d)tft  -\ /,. 


Fig.   173. 

D.  Crushing  four  rivets  and  shearing  one: 

nd* 

Resistance  =  \dtfc  -\ fs. 

4 

E.  Crushing  five  rivets: 

Res.stance  =  4dtfc  +  dtcfc. 

The    diameter    of    rivet  will    be    found    by  equating  the 
resistances  A  and  C. 

.  :  (P  -  d)tft  =  (P-  2d)tft  +  —/]. 

.      ,      ¥ft       4  X  f\  X  55.000 
.'.  a=  —=  = =  0.68. 

7Tfs  7:45,000 


370  STEAM-BOILERS. 

The  rivet  which  was  used  was  13/16  of  an  inch  when  driven. 

There  are  several  methods  in  which  we  may  find  the  way 
in  which  the  joint  will  fail,  and  then  find  therefrom  the  effi- 
ciency. One  is  that  shown  on  page  215  by  assuming  a  pitch 
and  calculating  the  resistance  of  the  joint  to  failure  in  each 
of  the  five  several  ways.  Another  method  is  to  equate  the 
five  several  resistances  two  and  two  and  calculate  the  pitch; 
the  least  pitch  thus  found  must  not  be  exceeded.     Thus 

Equating  B  and  C, 

4  4 

At    ft 

= ^Xiii52°  +  2XI3=9.4. 

7  ^  55,ooo  '  16 

4X4 
16 

Equating  A  and  B, 

(l>_*y/(  =  22*!/. 

4 
At   f 

v         4    W      45,000  ,  [3 
7  55,000  '  16 

4X4 
16 

Equating  A  and  D, 

{P-d)tf  =  Adtfc+  — '/.. 
A 


BOILER    DESIGX.  371 

.:.P  =  *£+?£xj+<l 

ft  \t         ft 

3.1416  x  (i§) 
13   95,000  ) \i6'   45,000   13  _ 

-4X^X"5?^o  '    ~  7       -X55>ooo+i6-7'4- 

4Xl6 

Equating  A  and  E, 

(P-d)tft  =  4dtfe  +  dtcfe. 

13    95,000    13/16x3/8    95,000    13      £ 

=  4  X  -|  X  — —  4-  — — ,  ,   '  ■  x  — —  +  -4  =  7-6. 
16       55,000  ;   16         ^  55,000  ]    16 

Here  /,,  the  thickness  of  the  cover-plate,  is  taken  to  be  3/8 
of  an  inch. 

The  greatest  allowable  pitch  at  the  outer  row  of  rivets  is 
evidently  7.4  inches. 

Instead  of  going  to  the  labor  of  solving  all  four  of  the 
above  equations,  we  may  find  by  some  other  method  how  the 
joint  is  likely  to  fail,  and  make  up  an  equation  involving 
those  resistances  only.  Thus  a  rivet  in  the  outer  row  may 
fail  by  shearing  or  by  crushing  at  the  cover-plate,  which  is 
here  made  thinner  than  the  shell-plate.  Equating  the  re- 
sistances of  the  two  methods,  we  have 

4 
or  for  a  cover-plate  3/8  of  an  inch  thick 

7t  45,000 

A  rivet  1.01  inch  in  diameter  will  consequently  be  just  as 


372 


STEAM-BOILERS. 


likely  to  fail  by  crushing  as  by  shearing.  But  the  resistance 
to  shearing  increases  as  the  square  of  the  diameter,  while  the 
resistance  to  crushing  increases  as  the  diameter.  It  is  there- 
fore evident  that  a  rivet  larger  than  i.oi  of  an  inch  will  fail  by 
crushing,  while  a  smaller  rivet  will  fail  by  shearing. 

A  similar  calculation  at  the  inner  row,  when  the  rivet 
bears  against  a  cover-plate  both  inside  and  outside,  and  will 
consequently  crush  against  the  shell-plate,  gives 

Js  =  tdfc\ 

4 

^=2XAx95^oo  =  a6< 
7i  45,ooo 

Here  a  rivet  larger  than  o.6  will  crush,  and  one  smaller 
will  shear.  It  is  now  evident  that  a  13/16  rivet  will  shear 
at  the  outer  row  and  will  crush  at  the  inner  row.  That  is,  for 
this  joint  the  failure  will  occur  by  the  method  D,  but  not  by 
the  methods  B  or  E.  Then  equating  the  resistances  A  and  D, 
and  solving  for  P,  we  get  for  the  pitch  at  the  outer  row  7.4 
inches  as  before.  The  corresponding  pitch  at  the  calking 
edge  of  the  outer  cover-plate  is  3.7  inches;  we  will  choose  for 
that  pitch  3-f  inches,  making  the  pitch  at  the  outer  row  y-\ 
inches. 

The  efficiency  of  the  joint  is 

P-d „7\-\% 


100 =  100  X  — —  =  88.8  per  cent. 

P  7\ 


In  the  preceding  article  the  apparent  factor  of  safety 
based  on  the  whole  strength  of  the  shell-piate  is  5.35.  Al- 
lowing for  the  efficiency  of  the  longitudinal  joint,  the  real 
factor  of  safety  when  the  boiler  is  new  is 


0.888  X  5-35  =  4-75- 


BOILER  DESIGN. 


373 


With  this  style  of  joint  the  shell-plate  is  protected  from 
corrosion  by  the  inner  cover-plate,  and  the  joint  will  lose 
little  if  any  efficiency  from  corrosion.  If  it  be  assumed  that 
the  plate  loses  1/16  of  an  inch  by  corrosion  during  the  life 
of  the  boiler,  then  the  strength  of  the  plate  will  be  one 
seventh  less  after  corrosion,  and  the  corresponding  factor  of 
safety  will  be 

5.35  X  f  =  4-6, 

which  may  be  considered  to  be  sufficient. 

Ring-seam. — The  stress  on  a  transverse  section  of  a 
homogeneous  hollow  cylinder  from  internal  fluid  pressure  is 
one  half  the  stress  on  a  longitudinal  section.  It  will  in  gen- 
eral be  found  that  a  single-  or  a  double-riveted  ring-seam  is 
sufficient  for  any  cylindrical  boiler-shell.  Marine  boilers 
commonly  have  double-riveted  ring-seams;  externally-fired 
horizontal  boilers  seldom  have  the  shell  more  than  half  an 
inch  thick,  and  for  that  thickness,  or  less,  single-riveted  ring- 
seams  are  used. 

It  is  found  in  practice  that  ring-seams  of  horizontal  ex- 
ternally-fired boilers  may  have  a  pitch  of  about  2T3F  inches  for 
all  thicknesses  of  plate  from  1/4  to  1/2  of  an  inch.  The 
diameters  of  rivets  for  such  seams  may  be  made  about  the 
size  given  in  the  following  table : 

Thickness  of  plate \         T5F  f  T7¥  $ 

Diameter  of  rivet £  j£  f  1  i 

The  ring-seam  in  question  has  a  circumference  of  about 

3.1416  X  60  =  188.2 

inches,  which  will  allow  us  to  use  84  rivets  with  a  pitch  of 
about  2.24  inches.  This  joint  will  fail  by  shearing  the  rivets. 
The  efficiency  of  the  joint  is  consequently  the  ratio  of  the 
resistance  of  a  single   rivet  to  shearing,  to  the   resistance  of 


374  STEAM-BOILERS. 

a  strip  of  plate  as  wide  as  the  pitch.  Consequently  the 
efficiency  is 

nd% 
4  ^=iX  3-I4I6  X  (j|)8  X  45.QOO  __ 
ptft  2.24  X  TV  X  55,000  "  *433' 

which  is  more  than  half  of  the  efficiency  of  the  longitudinal 
seam,  and  will  consequently  be  sufficient. 

Lap. — The  lap,  or  distance  from  the  centre  of  the  rivet  to 
the  edge  of  the  plate,  is  usually  taken  as  1.5  times  the  diam- 
eter of  the  rivet  used,  which  makes  the  distance  of  the  edge 
of  the  hole  from  the  edge  of  the  plate  equal  to  the  diameter 
of  the  rivet.  For  the  single-riveted  ring-seam  this  makes  the 
lap  equal  to 

1-5  X-Hr  =  l-22- 

It  is  customary  to  calculate  the  width  of  lap  required  on 
the  assumption  that  the  metal  between  the  rivet  and  the  edge 
of  the  plate  may  be  treated  as  a  beam  of  uniform  depth,  fixed 
at  the  ends  and  loaded  at  the  centre  by  the  force  which  would 
be  required  to  shear  or  crush  the  rivet,  taking,  of  course,  the 
larger.  The  width  of  the  beam  is  the  thickness  of  the  plate, 
the  depth  is  the  distance  from  the  edge  of  the  hole  to  the 
edge  of  the  plate,  and  the  length  is  the  diameter  of  the  rivet. 

Rivets  in  single-riveted  seams  fail  by  shearing.  The  load 
is  consequently  the  shearing  resistance 

ltd* 
4   U 

The  maximum  bending  moment  for  a  beam  of  uniform 
section  fixed  at  the  ends  and  uniformly  loaded  is  equal  to 
the  load  multiplied  by  one  eighth  of  the  span.  The  moment 
of  resistance  is  equal  to 

4 


BOILER    DESIGN 


37 


in  which /is  the  cross-breaking  strength  (about  55,000),  /is 
the  moment  of  inertia  of  the  section,  and  y  is  the  distance  of 
the  most  strained  fibre  from  the  neutral  axis.      Here  we  have 

,       /7/3  h 

I  =  — ,     y=  -, 
122 

representing  the  distance  from  the  edge  of  the  hole  to  the 
edge  of  the  plate  by  //. 

Equating    the    bending    moment    to   the   moment   of   re- 
sistance, 

4  6 


-*y« 


3  x  3-Hi6  X  13        45.000 

X  =  0.77 


s  1         d  5  5>ooo 

l6 

for  the  case  in  hand.       The  lap  is  consequently 

.     1  !3  o 

o./7  +-  X  4  =  i-i8 
2        16 

inches  for  the  ring- seam,  which  is  somewhat  less  than  that  by 
the  arbitrary  rule  that  it  should  be  once  and  a  half  the  diam- 
eter. 

A  similar  calculation  for  the  cover-plates  with  the  same 
diameter  of  rivet,  but  with  a  plate  3/8  of  an  inch  thick,  gives 
for  the  lap  1.24  or  1  j-  of  an  inch,  while  the  arbitrary  rule  gives 
1.03  of  an  inch.  It  is  probable  that  the  lap  may  be  consider- 
ably smaller  than  is  given  by  the  calculation  by  the  beam 
theory,  but  for  lack  of  direct  experimental  knowledge  on  this 
question  it  is  not  wise  to  make  the  lap  much  less  than  the 
calculation  gives;  we  will  consequently  use  \\  of  an  inch  for 
the  lap  of  the  cover-plates. 


76 


STEAM-BOILERS. 


The  rivets  of  the  inner  rows  pass  through  both  cover-plates 
and  are  in  double  shear,  and  consequently  fail  by  crushing 
as  is  shown  on  page  372.  The  load  to  be  used  tor  calculating 
the  lap  is  therefore  the  resistance  to  crushing  in  front  of  the 
rivet;  that  is,  we  here  have  for  the  load  tdfc.  The  equation 
of  bending  moment  and  moment  of  resistance  gives 

1  ttf 


A  =  <u/&  =  13/3  X  95.000  = 

V  4/      i6y  4  x  45,000 

The  lap  is  consequently 

1        13 
0.926  4--  X  ->  =  1.27, 

y       '    2       16  ' 

or  a  little  more  than  1^.      The  lap  used  is  if  of  an  inch. 

Tube-sheet. — The  next  step  in  the  design  is  to  lay  out 
the  tube-sheet  on  the  drawing-board.  If  possible,  the  tubes 
should  be  arranged  in  horizontal  and  vertical  rows  as  shown 
on  Plate  I.  The  distance  between  the  tubes  should  not  be 
less  than  three  fourths  of  one  inch ;  one  inch  is  better.  On 
Plate  I  the  horizontal  rows  are  spaced  one  inch  apart,  while 
the  vertical  rows  are  only  three  fourths  of  an  inch  apart ;  wider 
spacing  for  horizontal  rows  is  more  favorable  for  the  free  cir- 
culation of  water  and  the  disengagement  of  steam.  The  cir- 
culation is  improved  by  having  a  space  in  the  middle  as  shown 
on  Plate  I 

If  a  very  large  number  of  tubes  are  required  for  a  given 
boiler,  they  may  be  arranged  in  vertical  rows  and  in  rows  at 
30°  with  the  horizon,  as  on  Plate  II.  This  arrangement  is 
commonly  used  for  locomotive  boilers,  but  is  not  favored  for 
stationary  boilers. 

The  common  range  of  fluctuation  allowed  for  the  water- 


BOILER  DES1GX. 


line  with  this  type  of  boilers  is  six  inches,  three  above  and 
three  below  the  mean  water-level.  The  tops  of  the  tubes  arc 
set  about  three  inches  below  low  water-level. 

The  tubes  should  nowhere  be  nearer  than  three  inches 
from  the  shell,  and  the  bottom  row  should  be  from  four  to  six 
inches  from  the  bottom  of  the  boiler. 

The  hand-hole  near  the  bottom  of  the  head  should  be 
placed  as  low  as  possible;  the  flat  surface  for  the  gasket  should 
be  at  least  3/4  of  an  inch  wide.  No  tube  should  be  nearer 
than  an  inch  from  its  edge. 

The  tube  plate  is  usually  from  1  16  to  1  8  of  an  inch 
thicker  than  the  shell-plating.  The  internal  radius  of  the 
flange  should  not  be  less  than  half  an  inch.  For  plates  half 
an  inch  thick  or  less  the  outside  radius  is  commonly  made  one 
inch. 

In  applying  these  principles  to  the  tube-sheet  for  a  boiler 
60  inches  in  diameter,  as  shown  on  Plate  I,  it  appears  that  84 
tubes  may  be  used,  spaced  four  inches  horizontally  and  3f- 
vertically  and  with  a  space  at  the  middle  for  circulation,  pro- 
vided that  the  top  of  the  upper  row  of  tubes  is  d\  inches 
above  the  centre-line  of  the  boiler.  This  brings  the  water- 
level 

6^+6=  I2£ 

inches  above  the  middle  of  the  boiler,  instead  of  1 1.3  as  cal- 
culated on  page  329;  that  is,  the  water-level  is  raised  1.2  of 
an  inch  or  1/10  of  a  foot.  At  12  inches  above  the  middle, 
the  boiler  is  about  4^  feet  wide;  the  layer  of  water  added  has 
consequently  a  volume  of 

1/10  X  4-5  X  16=  7.2 

cubic  feet.  The  effect  is  to  reduce  the  steam-space  from  80 
cubic  feet  (see  page  363)  to  72.8  cubic  feet.  But  the  rule 
used  gave  from  64  to  80  cubic  feet,  so  that  72.8  cubic  feet  is 
a  fair  allowance.  If  the  tubes  were  spaced  nearer  together 
in   the   horizontal   rows  and   the   space  for  circulation   were 


378 


STEAM-BOILERS. 


omitted,  the  required  number  of  tubes  could  be  easily  provided  for 
without  raising  the  water-level.  If  in  any  case  a  satisfactory  ar- 
rangement of  tubes  cannot  be  made  with  the  diameter  assumed 


from  preliminary  calculations  of  steam-  and  water-space,  or  from 
some  other  method,  then  a  larger  diameter  must  be  usedc 

If  a  manhole  is  put  in  the  front  head  the  tube-sheet  is  as 
shown  in  Fig.  174.     There  are  now  74  tubes  instead  of  84,  and 


BOILER    DESIGN.  379 

the  heating-surface  is  reduced  by  [16.5  square  feet,  leaving  a 
total  of  978.8  square  feet,  or  about  12.5  square  feet  to  a  horse- 
power. The  head  under  the  tubes  is  stayed  by  angle  irons  tied 
to  the  head  by  two  through  rods.  This  staying  is  figured  in  the 
same  manner  as  the  channel-bars,  which  are  considered  later  in 
this  chapter. 

Area  of  Uptake. — The  area  of  the  uptake,  like  the  total 
area  through  the  tubes,  is  made  from  1/7  to  1/8  of  the  grate- 
area.  On  page  326  the  area  through  the  tubes  was  found  to 
be  492  square  inches.  The  uptake  may  be  made  12  inches 
deep,  measured  from  front  to  rear.      It  will  then  be 

492  -f-  12  =41 

inches  wide,  measured  transversely.  The  opening  through 
the  top  of  the  projecting  shell  at  the  front  end  will  be  made 
12  inches  deep,  as  shown  on  Plate  I,  and  must  be  cut  down 
till  it  is  41  inches  wide.  The  projecting  end  of  the  shell  is 
made  long  enough  so  that  a  space  of  about  one  inch  is  left 
between  the  uptake  and  the  calking  edge  of  the  front  tube- 
sheet. 

Length  of  Sections. — The  length  of  the  rings  or  sections 
of  the  cylindrical  shell  is  limited  by  the  reach  of  the  riveting- 
machine  and  by  the  width  of  plate  obtainable.  The  sec- 
tions are  often  made  the  same  length,  though  there  is  no  other 
reason  for  this  than  the  convenience  in  ordering  material. 
The  two  rear  sections  on  Plate  I  are  each  made  68  inches  from 
centre  to  centre  of  riveted  joints,  or,  allowing  1^  of  an  inch 
for  lap  at  each  end,  the  plates  when  finished  are  70^  inches 
wide       The  front  section  is 

•     14+  54f  +  a  =  69| 

inches  wide.  In  this  case  the  plates  could  all  be  ordered 
about  72  inches  wide. 

The  front  course  which  comes  over  the  fire  is  an  outside 
course,  so  that  the  flames  may  not  strike  directly  against  the 


380  STEAM-BOILERS. 

edge  of  the  plate  at  the  ring-seam.  The  length  of  the  grate 
is  commonly  about  one  third  of  the  length  of  the  boiler, 
which  brings  the  first  ring-seam  over  the  bridge,  where  the  fire 
is  the  hottest.  It  is  well  to  avoid  this  by  making  the  front 
section  shorter,  and  the  other  sections  longer. 

Manholes,  Hand-holes,  and  Nozzles.  —  These  fittings 
should  be  strong  enough  and  stiff  enough  to  carry  the  stresses 
which  come  from  the  direct  steam-pressure  and  from  the  ten- 
sion in  the  pieces  to  which  they  are  fastened ;  for  example, 
the  manhole-ring  must  be  able  to  take  the  place  of  the  piece 
of  plate  cut  away  at  the  hole. 

All  these  fittings  can  now  be  bought  in  the  form  of  steel 
forgings,  made  by  a  hydraulic  flanging  or  forging  machine. 
Gun-iron  and  cast  steel  are,  however,  much  used. 

The  determination  of  stresses  in  a  manhole-ring,  even  if 
appioximate  methods  are  used,  is  both  difficult  and  uncertain, 
and  will  not  be  considered  here.  Forms  and  dimensions  that 
have  been  used  in  good  practice  may  be  taken  for  a  guide  in 
designing.  A  rule  used  by  boiler-makers  for  forged  ringst 
which,  like  that  shown  on  Plate  I,  lie  close  to  the  shell-plate, 
is  to  make  the  section  of  the  ring,  exclusive  of  the  lip,  equal 
at  least  to  the  section  of  the  plate  cut  away.  The  aid  given 
by  the  lip  against  which  the  cover  bears  is  considered  to 
offset  eccentric  loading,  etc.  The  ring  of  a  steam-nozzle  may 
be  treated  in  the  same  way,  though  it  is  more  efficiently  aided 
by  the  cylindrical  portion.  Gun-iron  manhole-rings  should 
be  1  \  of  an  inch  thick,  and  nozzles  may  be  i^  of  an  inch  thick. 

An  approximate  calculation  of  the  stress  in  the  manhole- 
cover  may  be  made  by  treating  it  as  a  beam  supported  at  the 
ends  and  loaded  by  the  steam-pressure  and  by  the  pull  of  the 
bolt  at  the  middle;  this  last  must  be  assumed,  as  it  cannot  be 
known.  The  calculated  stress  will  be  in  excess  of  the  actual 
stress,  since  the  plate  is  supported  all  around.  The  handhole- 
plate  may  be  treated  in  a  similar  way.  Handhole-covers  are 
frequently  drawn  up  by  a  taper  key  instead  of  a  bolt  and  nut, 


BOILER  DESIGN.  381 

because  the  nut  is  exposed  to  the  fire,  and  often  cannot  be 
removed  with  a  wrench,  after  it  has  been  in  place  some  time. 

The  bearing-surfaces  of  the  manhole-cover  and  the  lip 
against  which  it  bears  should  be  machined  to  make  them 
true  and  smooth,  though  this  is  not  always  done.  The  hand- 
hole-cover  may  be  finished,  but  it  bears  directly  against  the 
plate,  which  of  course  is  not  finished.  In  any  case  the  joint 
is  made  tight  by  a  gasket  which  may  be  3/4  of  an  inch  wide 
for  the  hand-hole  and  from  that  width  to  an  inch  for  the  man- 
hole. 

Staying. — As  is  pointed  out  on  page  238,  the  calculation 
of  stresses  in  a  flat  plate  supported  at  intervals  can  be 
determined  only  by  the  application  of  the  theory  of  elasticity  ; 
and  the  only  determinate  case  is  that  in  which  the  supported 
points  are  in  equidistant  rectangular  rows,  dividing  the  sur- 
face into  squares.  This  case  applies  directly  to  the  staying 
of  the  fire-box  of  a  locomotive  by  stay-bolts.  Whatever 
system  of  arranging  the  supported  points  is  finally  chosen,  it 
is  convenient  to  make  a  calculation  for  the  determinate  case, 
with  the  points  in  equidistant  rows,  in  order  to  get  a  standard 
with  which  the  chosen  system  may  be  compared. 

The  equation  for  finding  the  stress  in  a  flat  plate  supported 
at  points  in  equidistant  rectangular  rows  is 

2d1 

in  which  a  is  the  distance  of  points  in  a  row,  t  is  the  thickness 
of  the  plate,  and  p  is  the  steam-pressure  in  pounds  per  square 
inch.  In  the  design  in  hand  t  =  9/16  of  an  inch  and  p  = 
150  pounds.     Assuming 

/=iV  X  55,ooo=  5500, 
and  solving  for  a,  we  have 


1 9  /**          /9X5500  X9X9  . 

a  =  \  /  — r  =  \  /  ~tt w — ~^~r, — ^  =  7  +  inches. 

\   2  p        y   2X150X  16X  16       '    ' 


382  STEAM-BOILERS. 

If  the  distance  between  supported  points  is  made  less  than 
7  inches,  whatever  the  system  of  arrangement  may  be,  we 
may  be  confident  that  the  stresses  will  not  exceed  5500 
pounds;  in  this  case  stresses  in  the  plate  are  due  only  to  the 
pressure  on  the  plate,  since  the  shell  of  the  boiler  is  self-sup- 
porting. 

In  the  several  ways  of  staying  the  flat  ends  of  boilers 
shown  on  pages  155  to  159  the  plate  is  riveted  to  channel- 
bars,  P.ngle-irons,  or  crowfeet,  which  in  turn  are  supported  by 
stay-rods.  The  rivets  are  in  direct  tension,  and  are  subject  to 
initial  stresses  due  to  the  contraction  when  they  cool;  it  is 
customary  to  limit  the  apparent  working  stress  to  6000 
pounds.  Rivets  less  than  3/4  of  an  inch  are  seldom  used, 
since  in  practice  they  are  found  to  be  too  much  affected  by 
initial  stress  due  to  cooling.  Large  rivets  are  also  considered 
to  be  undesirable.      We  will  choose  here  13/16  for  the  rivets. 

If  each  rivet  sustains  the  pressure  on  a  square  a  inches 
wide,  then  the  stress  per  square  inch  on  the  rivet  will  be 

—rfs=  150  X  a\ 

4 

in  which  d  is  the  diameter  and  fs  is  the  tensional  stress. 
Assuming  fs  =  6000  and  d=  13/16,  and  solving  for  «, ,  we 
have 


a>  =         '  X- 3  X  .3X6000  jnches 

y     150  x  16  x  16 

This  gives  for  the  limiting  distance  of  rivets  4.55  inches. 
Of  course  a  less  distance  may  be  used  if  convenient. 

In  some  cases  the  pitch  of  the  rivets  may  be  controlled  by 
the  system  of  staying.  For  example,  the  rods  used  with 
crowfeet  are  seldom  more  than  \\  of  an  inch  in  diameter, 
because  larger  rods  may  bring  too  large  a  local  stress  where 
they  are  riveted  to  the  cylindrical  shell.  Rods  one  inch  or 
an  inch  and  an  eighth  are  frequently  used.      A  double  crow- 


BOILER   DESJGX. 


3*3 


foot  has  four  rivets,  each  of  which  will  cany  one  fourth  of  the 
load  on  the  stay-rod.  A  stay-rod  1^  inches  in  diameter, 
and  limited  to  a  stress  of  7500  pounds,  may  carry  a  pull  in 
the  direction  of  its  length  ot 

7500  X  —     -  =  9204  pounds. 
4 

If  the  rod  makes  an  angle  of  20°  with  the  shell-plate,  the  pull 
which  it  will  exert  perpendicular  to  the  head  will  be 

9204  cos  200  =  9204  X  0.93969  =  8649 

pounds,  so  that  each  rivet  will  carry  about  2162  pounds.  If 
each  rivet  supports  a  square  having  the  side  a.t  exposed  to  the 
pressure  of  steam  at  150  pounds,  then 

2162  =  150  X  tf./\ 
or 

/2162 
a„  =  \  /  =  3-8  inches. 

Laying  out  Stays. —  Having  selected  the  form  of  staying 
to  be  used,  the  plan  must  be  laid  out  on  the  drawing-board, 
giving  proper  attention  to  practical  considerations,  such  as 
the  way  in  which  the  stays  are  to  be  inserted,  and  taking  care 
that  accessibility  is  not  too  much  interfered  with.  Fig.  140 
repeats  the  upper  part  of  the  head  of  the  boiler  shown  by 
Plate  I,  with  certain  additional  dotted  lines,  which  will  be 
referred  to  in  the  explanation  of  calculations.  The  area  to 
be  stayed  is  considered  to  be  limited  by  the  upper  row  of 
tubes,  and  by  a  dotted  line  drawn  i|-  of  an  inch  from  the 
inside  of  the  shell.  This  line  is  drawn  at  the  right  only;  it  is 
very  nearly  the  place  where  the  rounded  corner  of  the  flange 
joins  the  flat  surface  of  the  head.  The  distance  of  the  lowest 
row  of  rivets  from  the  top  row  of  tubes,  and  of  the  outer  row 
of  rivets  from  the  dotted  line,  may  be  as  great  as  their  maxi- 
mum distance  from  each  other.  Rivets  should  not  be  placed 
nearer  than  3  inches  from  the  tubes,  lest  the  expansion  of  the 


384  STEAM-BOILERS. 

tubes  should  start  leaks.  Rivets  may  be  placed  near  the 
dotted  line,  if  that  is  convenient.  For  example,  the  outer- 
most row  of  rivets  in  crowfoot  staying  (Fig.  57,  page  157) 
may  be  at  a  distance  #s  from  the  dotted  line;  for  \\  inch  stay- 
rods  a2  =  3.8  inches. 

The  method  of  staying  selected  consists  of  channel-bars 
riveted  to  the  head  and  supported  by  through-stays;  the 
upper  channel-bar  is  assisted  by  an  angle-iron.  The  channel- 
bars  selected  are  six  inches  wide,  and  the  horizontal  rows  of 
rivets  in  each  bar  are  3^  inches  apart,  which  brings  them  as 
near  the  flanges  of  the  bar  as  they  can  be  driven.  The  mid- 
dle of  the  lower  channel-bar  is  5f  inches  above  the  top  of  the 
tubes,  so  that  the  lowest  row  of  rivets  is 

5f-iX  3i  =  4 

inches  above  the  top  row  of  tubes.  But  the  plate  cannot  be 
properly  considered  to  be  rigidly  supported  at  a  line  drawn 
through  the  tops  of  the  tubes;  we  will  assume  the  line  of 
support  to  be  a  fourth  of  the  diameter  lower  down.  This 
makes  a  space  of  4f  inches,  instead  of  the  4.55  inches  calcu- 
lated for  13/16  rivets.  The  excess  may  be  considered  to  be 
offset  by  the  fact  that  the  other  row  of  rivets  in  the  channel- 
bar  is  only  3^  inches  distant. 

The  upper  channel-bar  is  placed  8  inches  above  the  lower 
one,  so  that  the  stay-rods  are 

30-(6i+5f+8)  =  9f 

inches  below  the  shell.  If  these  upper  rods  are  much  less 
than  10  inches  from  the  shell  access  to  the  boiler  will  be  diffi- 
cult. The  space  immediately  above  the  upper  channel-bar  is 
stayed  by  aid  of  an  angle-iron  which  is  riveted  to  the  channel- 
bar. 

The  distance  of  the  lower  row  of  rivets  in  the  upper  chan- 
nel-bar, above  the  upper  row  in  the  lower  bar,  is 

8  -  3i  =  4f 


BOILER  DESIGN.  3S5 

inches — the  same  as  the  distance  assigned  to  the  lowest  row 
of  rivets  above  the  assumed  line  of  support  at  the  top  row  of 
tubes.  The  top  row  of  rivets  in  the  angle-iron  is  only  a 
little  more  than  four  inches  below  the  dotted  boundary-line. 

Lower  Stay-rods. — In  order  to  determine  the  load  carried 
by  the  lower  stay-rods,  we  will  assume  that  half  the  load  on 
the  plate  between  the  lowest  row  of  rivets  and  the  top  row  of 
tubes  is  carried  by  the  rivets,  and  that  the  load  on  the  plate 
between  the  channel-bars  is  divided  equally  between  them. 
Now  we  have  assumed  that  the  line  of  support  at  the  tubes  is 
a  quarter  of  their  diameter  below  their  tops,  and  have  found 
this  line  to  be  4!  inches  below  the  lowest  row  of  rivets.  Half 
of  4!  is  2%.  Again,  the  distance  between  the  top  row  of  rivets 
in  the  lower  channel-bar  and  the  bottom  row  in  the  upper 
bar  is  4f  inches,  of  which  half  is  2f.  The  distance  apart  of 
the  two  rows  of  rivets  in  the  channel-bar  is  3|-  inches.  The 
total  width  of  plate  supported  by  the  channel-bar  may  there- 
fore be  considered  to  be 

2f  +  3i+  2f  =  8  inches. 

The  length  of  the  lower  channel-bar  at  the  middle  is  52 
inches,  as  measured  on  Fig.  142  ;  but  it  is  convenient  to  space 
the  rods  13^  inches  apart,  and  to  consider  the  bar  to  have  four 
equal  spaces,  which  leads  to  an  assumed  length  of  54  inches. 

The  load  on  the  lower  channel-bar  is  considered  to  be 

150  X  8  X  54  =  64,800  pounds. 

We  will  treat  the  channel-bar  as  a  continuous  girder  with 
four  equal  spaces  and  five  points  of  support,  of  which  three 
are  at  the  stay-rods  and  two  are  at  the  shell  of  the  boiler. 
By  the  theory  of .  continuous  girders  a  uniform  load  on  the 
channel-bar  would  be  distributed  among  the  five  points  of 
supports  as  follows:  At  each  point  of  support  at  the  shell 
11/112,  at  each  outer  stay-rod  32/112, at  the  middle  stay-rod 
26/112.  This  would  bring  on  each  of  the  outer  stay-rods 
T3T27  X  64,800  =  18,514  pounds. 


386  STEAM-BOILERS. 

Now  the  load  is  not  uniformly  distributed,  but  is  carried  in. 
part  by  the  rivets  and  in  part  by  the  nuts  and  thick  washers 
on  the  stay-rods;  but  the  actual  distribution  will  bring  a  less 
load  on  the  two  outer  stays,  so  that  the  assumpiion  of  the 
load  just  found  is  on  the  side  of  safety,  and  it  is  conveniently 
calculated. 

If  we  ascume  9000  pounds  for  the  working-stress  in  the 
stay-rods,  we  may  calculate  the  diameter  by  the  equation 

rrd'  __  18,510 
4  9000 

which  crives  for  the  diameter  something  less  than  if  of  an 
inch.  For  simplicity  all  five  stay-rods  will  be  the  same  size, 
namely,  if  of  an  inch — that  required  for  the  two  upper  stay- 
rods.  This  is  the  diameter  of  the  body  of  the  rod;  the  ends 
are  enlarged  to  l\  inches  where  the  thread  is  cut  for  the  nut. 

Lower  Channel-bar. — The  determination  of  the  actual 
stresses  in  the  channel-bar,  allowing  for  the  effect  of  the  nuts 
and  thick  washers  on  the  stay-rods,  is  very  uncertain.  On  the 
other  hand,  the  application  of  the  theory  of  continuous  girders 
with  a  uniform  load  may  not  give  us  a  stress  as  large  as  the 
actual  maximum  stress.  We  will  therefore  use  an  approxi- 
mate method,  which  will  give  a  stress  at  least  as  great  as  the 
greatest  stress  in  the  bar. 

For  this  purpose  we  will  assume  that  a  piece  of  the 
channel-bar  cut  by  the  lines  ab  and  cd  (Fig.  175)  may  be 
treated  as  a  simple  beam.  These  lines  ab  and  cd  are  drawn 
at  one  fourth  of  the  diameter  of  the  thick  washers  from  the 
centre  of  the  rod,  or  at 

\  X  5i=  ^ 
of  an  inch.  We  will  further  assume  that  the  load  on  the  pair 
of  rivets  A  and  B  is  due  to  the  pressure  of  the  steam  on  the 
area  efgh,  bounded  by  lines  drawn  half  way  between  them 
and  the  nearest  point  of  support.  Thus  eg  is  half-way 
between  the  rivets  and  the  line  ab,  gh  is  half-way  between  the 


BOILER   DESIGN. 


3*7 


388  STEAM-BOILERS. 

rivets  and  the  line  of  support  at  the  upper  row  of  tubes,  ef 
is  half-way  between  the  channel-bars,  and///  is  half-way  to 
the  next  pair  of  rivets.  The  rivets  are  4f  inches  from  the 
nearest  stay-rod,  and  are 

4f-  if  =3f 

inches  from  the  line  ab\  half  of  this  is  ii-g-  of  an  inch.  The 
two  pairs  of  rivets  are 

(I3f-  2  X  4f)  =  4 
inches  apart;  half  of  this  is  2  inches.      The  area  of  efgJi  is 

0H+2)X    8=29i 

square  inches;  and  the  steam-pressure  on  that  area  is 

29a  X   150  =  4425  pounds. 

This  is  the  load  due  to  each  pair  of  rivets  between  a  pair 
of  stay-rods;  and  since  the  rivets  are  symmetrically  placed, 
this  is  also  the  supporting  force  at  each  end  of  the  beam. 
Between  the  two  pairs  of  rivets  the  beam  is  subjected  to  a 
uniform  bending  moment,  equal  to  the  load  on  a  pair  of  rivets 
multiplied  by  their  distance  from  the  end  of  the  beam;  that 
is,  the  bending  moment  is 

4425  X  3f  =  M934- 
The  theory  of  beams  gives 

y 

in  which  M  is  the  bending  moment,  /  is  the  moment  of  inertia 
of  the  section  of  the  beam,  y  is  the  distance  of  the  most 
strained  fibre  from  the  neutral  axis,  and  /  is  the  stress  at  that 
fibre.  For  rolled-steel  channel-bars  we  may  use,  for/,  16,000 
pounds,  so  that  with  the  given  value  of  M  we  have 

16,000/  / 

14-934  =  — »    or     -  =  0.933. 


BOILER   DESIGX.  389 

Now  /and/  depend  on  the  form  and  size  of  the  section 
of  the  beam,  and,  conversely,  the  size  and  form  of  beam 
required  may  be  determined  from  them.  But  as  the  upper 
channel-bar  is  exposed  to  a  greater  bending  moment  and  con- 
sequently must  have  a  larger  section  than  is  required  for  the 
lower  bar,  we  will  defer  the  discussion  of  this  matter,  because 
it  is  convenient  to  make  the  bars  of  the  same  size. 

Upper  Stay-rods. — The  flat  surface  of  the  boiler-head 
above  the  lower  channel-bar  is  supported  by  the  upper 
channel-bar  aided  by  the  angle-iron  which  is  firmly  riveted  to 
it,  and  which  will  be  assumed  to  act  with  and  form  a  part  of 
the  channel-bar. 

Following  our  general  convention  that  the  pressure  on  a 
portion  of  the  head  between  two  lines  of  support  is  divided 
equally  between  them,  we  will  assume  that  the  load  on  the 
upper  channel-bar  is  due  to  the  steam-pressure  on  an  area 
bounded  at  the  bottom  by  a  line  half-way  between  the  upper 
and  lower  channel-bars,  and  at  the  top  by  an  arc  3^  inches 
inside  the  boiler-shell.  On  Fig.  175  half  of  this  area  is  rep-  • 
resented  by  jkl;  the  arc//t'  being  about  half-way  between  the 
root  of  the  flange,  shown  by  the  outer  dotted  boundary  line, 
and  the  adjacent  rivets.  In  place  of  the  areajk/  we  will  take 
the  rectangular  area  Imno,  bounded  at  the  end  by  a  line  at  the 
middle  of  the  end  of  the  channel-bar,  and  at  the  top  by  a  line 
mn  so  chosen  as  to  make  the  rectangular  area  larger  than  the 
area  it  replaces.  The  width  of  this  area,  /;;/,  is  9^  inches,  so 
that  the  load  per  inch  of  length  is 

91-  X  150  =  1387.5  pounds. 

The  upper  channel-bar  may  be  assimilated  to  a  continuous 
girder  with  three  unequal  spans;  the  middle  span  between 
the  stay-rods  is  15I  inches,  and  the  end  spans  between  the 
stay-rods  and  the  roots  of  the  flange  of  the  head  are  each 
\\\  inches.  This  makes  the  end  spans  nearly  3/4  of  the 
middle    span.      Now,   a  continuous   girder    uniformly    loaded 


39° 


STEAM-BOILERS. 


with  w  pounds  per  inch  of  length,  which  has  a  middle  span  / 
inches  long,  and  two  end  spans  §/  inches  long,  will  have  for 
the  end-supporting  forces  fffw/,  and  for  the  middle  support- 
ing forces  !!!«'/.  The  end  supporting  forces  are  provided 
by  the  shell,  which  is  abundantly  able  to  carry  them.  The 
stay-rods,  which  furnish  the  middle-supporting  forces,  must 
each  carry 

Mi  X  15^  X  I387-5  =21,083  pounds. 

Assuming  a  working-stress  of  9000  po"unds  per  square  inch 
for  the  stay,  the  area  of  the  section  for  a  stay  is 

21,083  -i-  9000  =  2.34 

square  inches.  The  corresponding  diameter  is  not  quite  i-j-^- 
of  an  inch.  As  rods  of  this  size  are  not  regularly  carried  in 
stock,  we  will  take  the  next  larger  regular  size,  namely,  if- 
of  an  inch.  This  is  the  size  mentioned  in  connection  with  the 
discussion  of  the  lower  stay-rods. 

Upper  Channel-bar. — The  calculation  of  the  stress  in  the 
upper  channel-bar  will  be  made  by  an  extension  of  the  same 
approximate  method  used  with  the  lower  channel-bar.  Since 
the  middle  span  is  wider  than  the  end  spans,  it  will  be  suffi- 
cient to  make  a  calculation  for  it  only.  The  calculation  is 
made  as  for  a  simple  beam  supported  at  the  ends,  the  points 
of  support  being  at  one  fourth  of  the  diameter  of  the  thick 
washer  from  the  middle  stay-rod,  that  is,  at  the  distance  of 
1 1  of  an  inch  from  the  stay-rod.  The  distance  between  the 
upper  stay-rods  is  15^  inches,  so  that  the  span  of  the  beam  is 

15^  —  2  X  if  =  i^f  inches. 

The  beam  is  assumed  to  be  loaded  with  concentrated  loads 
applied  at  the  rivets  C,  D,  E,  F,  G,  and  H  (Fig.  175);  the 
load  on  the  rivet  /  is  assumed  to  be  carried  by  the  stay-rod 
directlv,  and  is  not  included  in  this  calculation.      The  pair  of 


BOILER   DESIGN.  391 

rivets  D  and  E,  and  the  several  rivets  C,  G,  and  If,  are 
assumed  to  carry  the  load  due  to  the  pressure  on  the  areas 
marked  off  by  the  dotted  lines  on  Fig.  140,  each  line  being 
drawn  half-way  between  adjacent  supporting  points,  except 
that  the  arc  at  the  top  is  drawn  3J-  inches  from  the  shell,  as 
already  said.  The  calculation  of  the  loads  on  these  rivets,  of 
the  supporting  forces,  and  of  the  bending  moments  is  simple 
and  direct,  but  is  tedious  when  stated  in  detail.  We  will 
therefore  be  contented  to  say  that  the  bending  moment  at 
the  middle  of  the  beam  is  37,390.  Taking,  as  with  the  lower 
channel-bar,  a  working-stress  of  16,000  pounds,  we  have 

16,000/  / 

37,39<>  =  -— ,    or     -  =2.17. 

The  makers  of  steel  beams,  channel-bars,  and  angle-irons 
publish  handbooks  which  give  the  sizes  and  properties  of  the 
standard  forms,  including  the  moment  of  inertia  /  and  the 

ratio  -,  which  is  called  the  moment  of  resistance.      From  such 

y 

a  handbook  it  appears  that  the  moment  of  resistance  of  the 
channel-bar  6"  X  2^"  X  \"  is  1.08,  and  that  the  moment 
of  resistance  of  the  3^"  X  l"  angle-iron  is  1.55;  the  sum 
2.63  is  larger  than  the  required  moment  of  resistance  given 
above.  These  forms  are  consequently  used  as  shown  on 
Plate  I. 

Brackets. — The  boiler  shown  on  Plate  I  is  supported  on 
four  cast-iron  brackets,  each  of  which  is  10  inches  wide  in  the 
direction  of  the  length  of  the  boiler,  and  15^  inches  long 
measured  circumferentially.  Each  bracket  is  riveted  to  the 
shell  by  nine  rivets  15/16  of  an  inch  in  diameter.  Boilers 
over  16  feet  long  commonly  have  six  brackets.  The  brackets 
are  made  wide  and  long  in  order  that  the  local  strains  due  to 
carrying  the  weight  of  the  boiler  may  not  be  excessive.  The 
rivets  are  larger  than  are  used  about  the  boiler,  as  the  pitch  is 
not  restricted  as  in  a  calked  seam. 


592 


5  TEA  M-B01LERS. 


The  brackets  are  set  above  the  middle  line  of  the  boiler 
so  that  the  flanges  may  be  protected  by  brickwork.  In  the 
case  in  hand  they  are  3^  inches  above  the  middle;  as  much 
as  4%  inches  is  commonly  used. 

The  brackets  are  arranged  so  that  the  weight  of  the  boiler 
and  accessories  is  equally  divided  among  them,  and  so  that 
there  is  as  little  bending-moment  as  possible  on  the  shell  of 
the  boiler.  When  four  brackets  are  used  they  may  be  some- 
what less  than  a  fourth  of  the  length  of  a  tube,  from  the  tube- 
plates. 

The  load  on  the  brackets  may  be  estimated  by  calculating 
the  weight  of  the  boiler  when  entirely  full  of  water,  and  add- 
ing the  weight  of  all  parts  that  are  supported  by  the  boiler, 
such  as  pipes,  valves,  and  brickwork  or  covering,  that  may 
rest  on  the  boiler.  One  fourth  of  this  load  is  assigned  to  each 
bracket.  This  load  on  a  bracket  should  be  uniformly  dis- 
tributed over  the  bearing-surface  of  the  flange,  which  is  com- 
monly 8  or  9  inches  wide.  But  to  guard  against  the  effect  of 
unequal  bearing,  it  is  well  to  assume  the  bracket  to  bear  near 
the  outer  edge — say  two  inches  from  the  edge.  Such  an 
assumption  will  bring  the  bearing-force  on  a  bracket  on 
Plate  I,  10  inches  from  the  shell.  This  bearing- force  tends 
to  rotate  the  bracket  about  its  upper  edge,  and  this  tendency 
is  resisted  by  the  rivets  under  the  flange,  which  must  be  large 
enough  to  resist  the  resulting  pull  on  them.  The  other  rivets 
are  added  to  give  sufficient  resistance  to  shearing  all  the 
rivets.  There  are  seldom  less  than  nine  rivets  in  a  bracket, 
all  as  large  as  those  below  the  flange,  even  though  fewer  would 
suffice.  The  bracket  is  usually  made  of  cast  iron,  and  the 
dimensions  are  commonly  controlled  as  much  by  the  condi- 
tions required  for  a  sound  casting  as  by  calculations  for 
strength.  The  strength  may  be  calculated,  treating  it  as  a 
cantilever,  allowing  for  the  web  connecting  the  flange  to  the 
body  of  the  casting. 

Specifications   and    Contract. — The    engineer    intrusted 


BOILER   DESIGN.  ^g? 

with  the  design  of  a  boiler  prepares  a  set  of  working  drawings 
and  a  set  of  specifications  which  give  all  necessary  instructions 
concerning  the  material  to  be  used  and  the  methods  of  con- 
struction to  be  followed.  The  drawings  and  specifications 
form  a  part  of  the  contract  with  the  boiler-maker. 

Boiler-makers  commonly  design  standard  forms  of  boilers, 
and  in  answer  to  inquiry  will  furnish  a  statement  or  set  of 
specifications  for  a  desired  boiler  in  form  of  a  letter,  which 
letter  forms  the  contract  for  the  boiler.  On  the  next  page  is 
given  the  contract  and  specifications  for  the  boiler  shown  on 
Plate  I. 


194  STEAM-BOILER. 


.IRON  WORKS  CO. 


Boston,  Mass.,  Feb.   i,  1897. 


Gentlemen . 


Your  letter  of received.      We  will  build 

One  (/)  Horizontal  Tubular  Boiler.  One  Boiler,  viz.,  Sixty  (do)  inches  diameter  by 
seventeen  2/12  (17&)  feet  long.  Containing  84  Tubes  3  inches  diameter,  by  sixteen  (ib)  feet 
lone.  Shell  of  Boiler  of  O.  H.  Fire-box  Steel,  7/ 76"  thick,  not  less  than  35,000  vor  over  00,000 
lbs.  Tensile  Strength.     Not  less  than 56%  reduction  0/ area,  and  25%  elongation  in  8". 

Heads  of  Boiler  of  O.H.  Flange  Steel  a//6"  thick.  Longitudinal  Seams  Butt  Jointed, 
with  double  covering-plates,  Triple  Riveted.  Rivet-holes  drilled  in  place,  i.e.,  Rivet-holes 
punched  1/4"  small,  courses  rolled  up,  covering-plates  bolted  on  courses.  Heads  in  courses 
•with  all  holes  together  perfectly  fair.      Then  rivet-holes  drilled  to  full  size. 

Longitudinal  braces  without  welds,  with  upset  screw  ends. 

Two  (2)  or  three  (.?)  Lugs  on  each  side,  and  to  be  provided  with  wall-plates  and  expan- 
sion-rolls.    Manhole  (internal  frame)  on  top.      This  frame  a  steel  casting. 


Two  (2)  3"  Nozzle.?  on  top, 


A  Hand-hole  in  each  head,  Fusible   Safety  Plug  in   back  head.    Bottom  at  back  end 

reinforced  and  tapped  for  2"  blowout  

Internal  Feed  Pipe  placed  in  Boiler Co.'s  style, 

With  Boiler,  Castings  for  setting,  viz.;  C.  I.,  Overhung  Front,  Mouth-pieces, 
Division  Plates,  Grate  Bars,  shaking  pattern  00"  X60".  Grate  Bearers,  Ash-pit  Door  for 
the  brickwork,   Back  Return  Arched  T  Bars,  the  Anchor  Bolts  for  Front.      One  (1)  set  of 

six  (6)  Buckstaves  and  Tie  Rods  with  the  boiler.     With  the  Boiler  One  (1)  4" Pop 

Safety  Valve,  (3).?//'  Gauge  Cocks,  One  (1)  6"  Steam  Gauge,  One  (1)3/4"  Water  Gauge  and 

One  (1)  Combination  Column Boiler   tested  223  lbs.  per 

square  inch.     Inspected  and  Insured  in  the  sum  of  $400.00  for  one  year,  by Steam 

Boiler  Inspection  &  Insurance  Co 

The  Boiler  Castings  and  Fixtures  as  herein  specified  by  name,  delivered  F.  O.  B.  cars, 
or  at  vessel's  wharf,  or  on  sidewalk  of  building,  Boston,  Mass.,  for  the  sum  of  six  hundred 

and  seventy  (670.00)  dollars  net. 

Very  respectfully  yours, 

IRON  WORKS  CO. 

P.  S.— Specimens  will  be  furnished,  one  lengthwise  and  one  crosswise,  from  each  plate. 
To  be  at  least  iS"  lonir  and  planed  on  edge  1"  or  i\"  wide.  These  specimens  shall  show  no 
blowhole  defects  and  shall  bend  double  cold,  at  a  red  heat,  and  at  a  /tanging  heat. 


APPENDIX, 


!96 


APPEXDIX. 


HORIZONTAL  RETURN  TUBULAR 


No. 


14 
15 
16 

17 
18 

19 
20 
21 
22 

23 
24 
25 
26 

27 
28 

29 


32 
33 
34 
35 
36 
37 
38 
30 
40 
41 
42 
43 
44 

45 
46 

47 
48 
49 
50 


Horse- 
power. 


25 
33 
39 
55 
62 

49 
56 
67 
76 
86 
64 
73 
82 

87 

99 

112 

76 

87 
98 
124 
140 
155 
"3 
127 

141 

99 

111 

124 

U58 
178 
198 

i44 
162 
180 
129 

145 
161 
209 
232 

i95 
216 
182 
202 

257 
286 
236 
262 
215 
239 


Heat- 
ing- 
Surface 


254 
3°4 

403 
469 

604 
690 
548 
625 

739 
S44 
94U 
7°4 
803 

9°3 

875 

999 

1 1 23 

765 

873 

981 

1247 

1401 

1556 

ii33 

1273 

1414 

996 

1119 

1242 

158S 

1785 
1982 
1448 
1628 
1S07 
1292 
1452 
1612 
2090 
2321 
1952 
2167 
1821 
2022 

2579 
2864 
2367 
2629 

2155 
2302 


She!!. 


Diam- 
eter. 


56 
36 

42 
42 
48 
48 
48 
48 
54 
54 
54 
54 
54 
54 
60 
60 
60 
60 
60 
60 
66 
66 
66 
66 
66 
66 
66 
66 
66 
72 
72 


72 
72 
72 
72 
78 
78 
78 
78 
78 
78 
84 
84 
84 
84 
84 
84 


Length, 
O.  H. 


13 
13 
15 
U5 


Length, 
Flush. 


15 


17 
19 
U5 
17 
19 
U5 
17 
19 
15 
17 
19 
17 
19 
21 

i7- 
19 
21 

17 
19 


19 
21 

J7 
19 

21 
17 
19 
21 

19 
21 

19 

21 

19 
21 

19 
21 

19 
21 

19 


IS 

17 


17 
15 


19 

U5 


!9 

15 


IQ 


I'.J 


[9 


[9 


1Q 


Tube<. 


Length, 


14  o 

14  o 

16  o 

14  o 

16  o 

14  o 

16  o 

18  o 

14  o 

16  o 

18  o 

14  o 

16  o 

18  o 

14  o 

16  o 

18  o 

16  o 

18  o 

20  o 

16  o 

18  o 

20  o 

16  o 


20 

16 


16 

18 

20 

16 

18 

20 

18 

20 

18 


18 

20 

18 

20 

18 


Diam- 
eter. 


3 

3 

3 

3i 

3* 

3 

3 

3i 
3h 
3  J 


3 

32 

3  J 

32 

3 

3 

3 

3? 

3z 

32 

4 
4 
4 
3 


3h 
3* 

32 

4 

4 
4 
3 

3 

32 
32 

4 
4 
3 
3 

32 
32 

4 
4 


Number 


With 
Man- 
hole. 


74 
74 
74 
54 
54 
54 
94 
94 
94 
72 

72 

72 

54 

54 

54 

122 

122 

122 

94 

94 

94 

72 

72 

72 

144 

144 

ii4 
114 

92 
92 
180 
180 
140 
140 
no 
no 


With- 
out 

Man- 
hole. 

28 
28 
38 
38 

5° 

5° 

38 

38 

62 

62 

62 

5° 

5° 

5° 

82 

82 

82 

62 

62 

62 

104 

104 

104 

80 

80 

80 

62 

62 

62 

130 

J3° 

l3° 

102 

102 

102 

80 

80 

80 

U54 

154 

122 

122 

100 

100 

190 

190 

150 

150 

114 

114 


APPENDIX. 


397 


BOILERS. 

(ROBB-MUMFORD  BOILER  Co.) 

Thickness, 

1 25  Pounds. 

Thickness. 

I50  PoUndS 

1  Mates. 

Weights. 

Size 
of 

Safety 

Shell.  Heads 

Style 
Joint. 

Shell. 

Heads  ?tyto 

Joint. 

Valve 

Width  L'gth 

Boiler 
Only. 

Castings. 

Total. 

I  4 

3/8 
3/8 

D.I 

36 
36 

xo 

2730 
3120 

2020 

4760 
5200 

r/4 

D.L. 



2 

0^ 
36 

2080 

5  "' 

3/8 

D.B. 

11/32 

3/8  D.B. 

2 

42 

36 

4670 

2670 

7340 

5/i6 

3/8 

D.B. 

11/32 

3/8  |  D.B. 

2 

42 

42 

5270 

2740 

8010 

n/32 

7/16 

D.B. 

13/32 

7/16  D.B. 

zj 

48 

42 

6800 

3540 

10340 

11/32 

7/16 

D.B. 

13/32 

7/16 

D.B. 

0i 

48 

48 

758o 

4000 

1 1 580 

.!   32 

7/16  D.B. 

^3l32 

7/16 

D.B. 

2I 

48 

42 

6740 

3540 

10280 

11  32  7/16  D.B. 

13/32 

7/16 

D.B. 

A 

48 

48 

7520 

4000 

1 1  520 

11  32 

7/16  T.B. 

13/32 

7/16 

T.B. 

2j 

54 

48 

8120 

4300 

12420 

ii/32 

7/16  T.B. 

I3/32  7  "' 

T.B. 

3 

54 

54 

9100 

477° 

13S70 

11  32 

7  16  T.B. 

13/32  7/16 

T.B. 

3 

54 

60 

1 0000 

5X9° 

15190 

n/32 

716  T.B. 

13/32  7/16 

T.B. 

2§ 

54 

48 

8210 

4300 

12510 

11/32 

7  ,o  T.B. 

I3/32  7  "' 

T.B. 

3 

54 

54 

9210 

477° 

13980 

11.  32 

7  c6 

T.B. 

13/32  7/i6 

T.B. 

3 

54 

60 

101  20 

5190 

1 53 10 

3/8 

1/2 

Q.B. 

7/16  1  2 

Q.B. 

3 

60 

54 

10270 

4920 

1519° 

3/8 

1/2 

Q.B. 

7/16 

1/2 

Q.B. 

3 

60 

60 

11420 

53°° 

16720 

3/8 

1/2 

Q.B. 

7/16 

1/2 

Q.B. 

3 

60 

66 

12480 

594o 

18420 

3/8 

1/2 

Q.B. 

7/16  1  1/2 

Q.B. 

3 

60 

54 

10060 

4920 

14980 

3/8 

1/2 

Q.B. 

7/16  1/2 

Q.B. 

3 

60 

54 

1 1 180 

5170 

16250 

3/8 

1/2 

Q.B. 

7,16  1  2 

Q.B. 

3 

60 

60 

12200 

579° 

17990 

13/32 

1/2 

Q.B. 

15/32  1  2 

Q.B. 

3 

66 

60 

14500 

579° 

20290 

13/ 32 

Q.B. 

1;  '32  1  '2 

Q.B. 

3i 

66 

66 

15930 

6410 

22340 

13/32 

1/2 

Q.B. 

15/32  1/2 

Q.B. 

3\ 

66 

72 

17380 

6540 

23920 

13   3 2 

1/2 

Q.B. 

15/32  1/2 

Q.B. 

3 

66 

60 

14410 

579° 

20200 

13/32 

1/2 

Q.B. 

15/32  i  - 

Q.B. 

3 

66 

60 

15840 

6170 

22010 

J3/32 

1/2 

Q.B. 

15/32  1/2 

Q.B. 

3* 

66 

66 

17270 

6410 

23680 

13/32 

1/2 

Q.B. 

15/32  1/2 

Q.B. 

3 

66 

60 

14210 

5790 

20000 

13/32 

1/2 

Q.B. 

15/32 

1/2 

Q.B. 

3 

66 

60 

1 5610 

6170 

21780 

13/32 

1/2 

Q.B. 

r5/32 

1/2 

Q.B. 

3 

66 

60 

17020 

6170 

23190 

7/i6 

1/2 

Q.B. 

17/32 

9/16 

Q.B. 

3i 

72 

66 

17170 

6540 

2^710 

7/16 

1/2 

Q.B. 

17/32 

9/16 

Q.B. 

3i 

72 

72 

18910 

7290 

26200 

7,'i6 

1/2 

Q.B. 

17/32 

9/16 

Q.B. 

4 

72 

84 

20650 

758o 

28230 

7/i6 

1/2 

Q.B. 

17/32 

9/16 

Q.B. 

3\ 

72 

66 

1 7100 

6540 

23640 

7  16 

1/2 

Q.B. 

[7/32  9/16 

Q.B. 

3\ 

72 

72 

18820 

7290 

261 10 

7/16 

1/2  Q.B. 

17/32;  9/16  Q.B. 

3\ 

72 

78 

20560 

744o 

28000 

7/16 

1/2  Q.B. 

17/32!  9/16!  Q.B. 

3\ 

72 

66 

16960 

6540 

23500 

7/i6 

1/2  Q.B. 

,7  32  9/i6  Q.B. 

3\ 

72 

66 

18670 

7J5° 

25820 

7/16 

1/2  Q.B. 

[7/32  9/16  Q.B. 

3\ 

72 

72 

20390 

7290 

27680 

1/2 

9/16  T.B. 

g  16  9/16  Q.B. 

4 

78 

78 

22580 

8550 

3ll3° 

1/2 

9  t6  T.B. 

9/16 

9/16 

Q.B. 

4 

78 

90 

24620 

8860 

3348o 

1/2 

9  c6  T.B. 

9/16 

9/16 

Q.B. 

4 

78 

78 

22710 

8550 

31260 

1/2 

q  16  T.B. 

9  16 

9/16 

Q.B. 

4 

78 

84 

24770 

8660 

3343o 

1/2 

9/16  T.B. 

9/16  9/16 

Q.B. 

4 

78 

72 

22960 

8400 

51360 

1/2 

9/16  T.B. 

9/16  9/16 

Q.B. 

4 

78 

78 

25060 

8550 

336io 

1/2 

9/16  Q.B. 

19/32  5/8 

Q.B. 

4^ 

90 

84 

25700 

9440 

35MO 

1/2 

9/16  Q.B. 

19/32 

5/8 

Q.B. 

4l 

90 

96 

28100 

9790 

37890 

1/2 

9/16  Q.B. 

19/32 

5/8 

Q.B. 

4* 

90 

84 

25670 

9440 

35"° 

1/2 

9/16  Q.B. 

19/32 

5/8 

Q.B. 

4* 

90 

90 

28070 

9620 

5769o 

1/2 

9/16  Q.B. 

19/32 

5/8 

Q.B. 

4i 

90 

78 

25700 

9260 

54960 

1/2 

9/16  Q.B. 

19/32 

5/8 

Q.B. 

4* 

90 

84 

28110 

0440 

3755° 

39« 


APPEXDIX. 


APPEXDIX. 


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APPENDIX 


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APPENDIX. 


40 1 


Stirling  Boilers. — These  boilers  clean  from  the  side,  the 
same  as  the  B.  &  \Y..  and  only  two  can  be  set  together  without  a 
space  between.  If  necessary  the  boiler  may  be  set  without  a 
space  at  the  back,  but  it  is  advisable  to  have  at  least  3  feet 
back  of  the  rear  wall. 

These  boilers  are  also  built  with  attached  superheaters.  The 
superheater  is  placed  at  different  parts  of  the  setting,  according 
to  the  number  of  degrees  of  superheating  desired. 

The  following  table  gives  dimensions  of  this  boiler  for  different 
boiler  horse-powers. 

If  the  boiler  is  equipped  with  a  superheater,  deduct  10  per 
cent  from  the  rated  horse-power.  If,  however,  the  superheater 
is  flooded  the  capacity  of  the  boiler  is  increased  approximately 
7  per  cent  above  the  ratings  given. 

HORSE-POWER  OF  STIRLING  BOILERS. 
Arranged  with  Reference  to  Height  and  Width  of  Settings. 


Class. 

Wi.lt 
Sett 

h  of 

inc. 

B-!ow. 

P 

1  E 

B 

1  A  |  Q 

F 

1  R 

K 

L 

N 

Heiehr. 

Bat- 
tery.* 

feet. 

t  i'ii" 

1  5'  4*' 

Us'  3" 

iS'  8" 

|i8'  9"|i8'io" 

20'  7" 

I20'  8" 

21' 10" 

I22'  4" 

24'  6" 

Single. 

Depth 

ft   in. 

14'  0" 

18'  7" 

16'  3" 

14'  0" 

16'  o";i8'  9" 

*'  » 
16  9 

18'  2" 

17'  7" 

18'  3" 

18  10" 

5  6 

10 

5° 

... 

... 

50 

6  0 

1 1 

55 

75 

60 

6  6 

12 

65 

90 

70 

7  ° 

13 

75 

1 1 5 

100 

So 

"5 

i45 

140 

145 

150 

1  "5 

175 

7  & 

14 

«5 

130 

«5 

90 

130 

165 

155 

160 

170 

i«5 

195 

8  0 

'5 

95 

i45 

J-5 

100 

MS 

180 

175 

180 

i«5 

205 

2  20 

8  6 

16 

105 

160 

140 

1 10 

160 

200 

190 

200 

205 

230 

240 

9  0 

'7 

"5 

175 

!5° 

120 

175 

215 

205 

215 

225 

250 

260 

9  * 

18 

I25 

190 

165 

T3° 

190 

235 

225 

235 

245 

270 

285 

10  0 

19 

J35 

205 

175 

140 

205 

255 

240 

250 

260 

290 

3°5 

10  6 

20 

140 

220 

190 

150 

215 

270 

260 

270 

280 

310 

33° 

11  0 

21 

150 

230 

200 

160 

230 

290 

275 

2«5 

300 

33° 

35o 

11  6 

22 

160 

245 

215 

170 

245 

310 

295 

3°5 

3i5 

35o 

37° 

12  0 

23 

170 

260 

225 

180 

260. 

325 

310 

325 

335 

37° 

395 

12  6 

24 

1  So 

275 

240 

190 

275 

345 

33° 

34o 

355 

395 

4i5 

r3  ° 

25 

190 

290 

250 

200 

290 

360 

345 

360 

375 

4L5 

435 

1  5  6 

26 

200 

3°5 

265 

210 

305 

380 

360 

375 

39° 

435 

460 

14  0 

27 

210 

320 

275 

220 

320 

300 

380 

395 

410 

455 

480 

14  6 

28 

220 

335 

290 

230 

335 

4i5 

395 

410 

43° 

475 

5°5 

15  ° 

29 

230 

35° 

300 

240 

35° 

435 

415 

43° 

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*  The   horse-power  is   double   for   battery   \v 
alley  on  one  side;  battery  boilers  require  an  alley 


idth  shown.     Single  boilers  require  an 
on  both  sides. 


402  APPENDIX. 

Heine  Water  Tube  Boiler. — This  boiler  requires  a  space  at 
the  back  as  it  is  cleaned  from  the  ends.  Any  number  of  boilers  of 
this  type  can  be  set  side  by  side. 

The  space  in  front  of  the  boiler  should  be  sufficient  to  allow  of  the 
renewal  of  a  tube. 

The  accompanying  table  together  with  the  "Notes"  will  serve  to 
give  necessary  sizes  for  a  given  boiler  horse-power. 

Notes. 

The  length  of  setting  from  fire  front  to  rear  of  brickwork  is  always 
I  foot  4  inches  longer  than  the  length  of  the  tubes,  for  instance,  the 
setting  of  a  90  horse-power  boiler  is  1 7  feet  4  inches  long  and  a  101  horse- 
power boiler  is  19  feet  4  inches  long.  The  shell  with  manhead  extends 
about  15  inches  beyond  rear  of  setting,  so  that  if  possible  a  4-foot  space 
should  be  allowed  behind  the  setting  for  access  to  same.  In  special 
cases  the  manhole  is  placed  in  the  front  head,  or  an  opening  may  be 
made  in  the  building  wall  opposite  manhole,  in  which  case  2  feet 
behind  setting  will  be  sufficient.  The  width  of  setting  may  be  deter- 
mined by  adding  the  thickness  of  brick  walls  to  the  width  of  furnace. 
Thus,  three  101  horse-power  boilers  in  a  battery,  with  19  inches  side 
and  28  inches  division  walls,  will  be  19"+  53"+  28"+  53"+  28"+  53" 
-f  19"=  21'  1".  Existing  walls  may  be  utilized  where  space  is  limited, 
and  the  outside  walls  here  reduced  to  a  furnace  lining  9  or  10  inches 
thick. 

The  grate-surface  given  for  bituminous  coal  is  such  that  the  rating 
may  be  easily  developed  with  a  1  2-inch  draught  at  the  smoke  outlet. 
The  grate  area  given  for  anthracite  pea  coal  is  that  necessary  in  order 
to  develop  the  rating  of  the  boiler  with  1,  2-inch  draught  at  the  smoke 
outlet.  For  convenience  of  handling  it  is  advisable  to  limit  the  grate 
length  for  anthracite  coal  to  7  feet  6  inches.  "Where  this  does  not  give 
area  enough  for  the  desired  maximum  capacity  it  is  necessary  to  in- 
crease the  draught.  Standard  grate  lengths  are  6  feet  6  inches,  7  feet 
and  7  feet  6  inches. 

Safety-valves  are  provided  as  required  to  meet  local  inspection  law- . 


Babcock  and  Wilcox  Boilers. — These  boilers  clean  from  the 
side.     There  must  be  a  space  of  at  least  5  feet  between  each  set  of  two. 

The  tables  on  pages  405  and  406  give  space  taken  up  by  boilers  with 
vertical  headers.  For  inclined  headers,  any  number  of  tubes  high,  add 
3  feet  8  inches  to  the  length  given. 

A  double-deck  boiler  is  10  inches  higher  than  a  single-deck  boiler 
of  same  number  of  tubes  high. 

Space  must  be  left  in  front  of  the  boiler  to  enable  the  lowest  tube  to 
be  replaced. 


APPEXDIX. 


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APPENDIX. 


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APPENDIX. 
GREEN'S  FUEL  ECONOMIZER. 


407 


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10 

24-    2 

' 

40 

4800 

24,800 

2-5 

3  • 

440 

ro 

26-    7 

44 

5280 

27,780 

2  -5 

3  . 

480 

10 

29-   0 

tt 

48 

576o 

29.780 

2-5 

3  ■ 

S20 

10 

31-  S 

52 

6240 

32,240 

3 

3- 

560 

10 

33-io 

56 

6720 

34,720 

3 

4. 

600 

TO 

36-  3 

60 

7200 

37,200 

3 

4. 

640 

IO 

38-  8 

" 

64 

7680 

39,680 

3 

4. 

680     10 

41-   1 

1 

68 

8160 

42,160 

3 

4. 

720     10 

43-  6 

' 

72 

8640 

44,640 

4-5 

4. 

760     10 

4^-n 

" 

76 

9120 

47.120 

4.5 

4. 

3 
3 

800     10 

48-  4 

80 

9600 
i 

49.600     5 

4. 

«o8 


APPENDIX. 


STANDARD  SIZES  OF  STURTEVANT 

Ex- 

General Dimensions. 

Ma- 
chine 

No. 

of 

Pipes. 

No. 
of 
Sec- 
tions. 

No.  of 
Pipes  in 
Section. 

ternal 
Heat- 
ing- 
surface. 

Capacity 

in 
Pounds 

of 
Water. 

Length. 

Width. 

Height  in  Feet  and 
Inches. 

No. 

Section. 

Section 
and 

Sq.  ft. 

Ft. 

In. 

Ft.    In. 

Gearing. 

I 

32 

8 

4 

400 

2,016 

4 

IO 

3  t(2h 

10      2J 

12      6 

2 

48 

12 

4 

600 

3>°24 

7 

3 

" 

3 

64 

16 

4 

801 

4,032 

9 

8 

" 

4 

80 

20 

4 

IOOI 

5>°4° 

12 

1 

" 

5 

96 

24 

4 

1 201 

6,048 

14 

6 

<< 

6 

112 

28 

4 

1 401 

7>°56 

16 

11 

" 

7 

128 

32 

4 

1601 

8,064 

19 

4 

<  < 

8 

40 

8 

5 

499 

2,520 

4 

10 

3  J°h 

IO       2\ 

12       6 

9 

60 

12 

5 

749 

3-78o 

7 

3 

1 1 

IO 

80 

16 

5 

999 

5.040 

9 

8 

t« 

ii 

100 

20 

5 

1248 

6,300 

12 

1 

1 1 

12 

120 

24 

5 

1499 

7,560 

14 

6 

<< 

13 

140 

28 

5 

1747 

8,820 

16 

11 

n 

14 

160 

32 

5 

1997 

10,080 

!9 

4 

•  1 

i5 

180 

36 

5 

2247 

",34o 

21 

9 

<« 

16 

200 

40 

5 

2496 

12,600 

24 

2 

<( 

i7 

72 

12 

6 

897 

4,536 

7 

3 

4<<6} 

IO      2J 

12       6 

18 

96 

16 

6 

1 196 

6,048 

9 

8 

II 

19 

120 

20 

6 

1496 

7,56o 

12 

1 

«l 

20 

144 

24 

6 

1795 

9,072 

14 

6 

•  1 

21 

168 

28 

6 

2094 

10,584 

16 

11 

II 

22 

192 

32 

6 

2393 

12,096 

19 

4 

II 

23 

216   ' 

36 

6 

2692 

13,608 

21 

9 

II 

24 

240 

40 

6 

2991 

15,120 

24 

2 

II 

25 

264 

44 

6 

3290 

16,632 

26 

7 

II 

26 

288 

48 

6 

3589 

18,144 

29 

0 

II 

27 

112 

16 

7 

1394 

7,056 

9 

8 

5  t*\ 

10     2J 

12       6 

28 

140 

20 

7 

1743 

8,820 

12 

1 

II 

29 

168 

24 

7 

2092 

10,584 

14 

6 

II 

3° 

196 

28 

7 

2440 

12,348 

16 

11 

II 

3i 

224 

32 

7 

2789 

14,112 

19 

4 

(1 

32 

252 

36 

7 

3137 

15,876 

21 

9 

II 

33 

280 

40 

7 

3486 

17,640 

24 

2 

II 

34 

308 

44 

7 

3835 

19,404 

26 

7 

II 

35 

336 

48 

7 

4183 

21,168 

29 

0 

II 

36 

364 

52 

7 

4532 

22,932 

3i 

5 

II 

37 

392 

56 

7 

4880 

24,696 

33 

10 

II 

38 

128 

16 

8 

1592 

8,064 

9 

8 

5  fj">} 

10     2J 

12       6 

39 

160 

20 

8 

1990 

10,080 

12 

1 

II 

40 

192 

24 

8 

2388 

12,096 

14 

6 

II 

41 

224 

28 

8 

2786 

14,112 

16 

11 

II 

42 

256 

32 

8 

3185 

16,128 

l9 

4 

II 

43 

288 

36 

8 

3583 

18,144 

21 

9 

II 

44 

320 

40 

8 

398i 

20,160 

24 

2 

II 

45 

352 

44 

8 

4379 

22,176 

26 

7 

II 

46 

384 

48 

8 

4777 

24,182 

29 

0 

II 

4? 

416 

52 

8 

5175 

26,198 

31 

5 

II 

48 

448 

56 

8 

5573 

28,224 

33 

10 

II 

49 

480 

60 

8 

597i 

30,240 

36 

3 

II 

APPENDIX. 


409 


STANDARD 

ECONOMIZERS. 

No. 

o< 

Pipes. 

No. 
of 

Sec- 
tions. 

No.  of 
Pipes  in 
Section. 

Ex-     _ 
ternal    Capacity 
Heat-          In 
ing-        bounds 
surface.     ,,."' 

\\  ater. 

<  leneral  1  limensions, 

Ma- 
chine 

Length. 

Width. 

Height  in  Feet  ant 
Inches. 

No. 

Section. 

Se<  ii"n 
and 

Sq.  ft. 

Ft. 

In. 

Ft.    In 

( tearing. 

5° 

180 

20 

9 

2,237      11,340 

12 

1 

6     6* 

IO       2\ 

12     6 

51 

216 

24 

9 

2,685      I3,6o8 

14 

6 

'* 

" 

" 

52 

252 

28 

9 

3,132      15,876 

16 

11 

" 

t  i 

" 

53 

288 

32 

9 

3,580      18,144 

19 

4 

" 

" 

•■ 

54 

324 

36 

9 

4,027      20,412 

21 

9 

" 

" 

" 

55 

360 

40 

9 

4,475      22,68o 

24 

2 

•* 

" 

" 

56 

396 

44 

9 

4,922      24.948 

26 

7 

" 

" 

" 

57 

432 

48 

9 

5>37° 

27,216 

29 

0 

" 

"' 

" 

58 

468 

52 

9 

5,817     29,484 

3i 

5 

" 

" 

•« 

59 

5°4 

56 

9 

6.265     3J.752 

33 

10 

" 

" 

" 

60 

540 

60 

9 

6,712    34,020 

36 

3 

" 

" 

•  ' 

61 

576 

64 

9 

7,160    36,288 

38 

8 

" 

" 

62 

200 

20 

10 

2,484     12,600 

12 

1 

7i(2i 

IO       2i 

12     6 

63 

240 

24 

10 

2,q8i     15,120 

14 

6 

" 

•  « 

64 

280 

28 

10 

3.478 

17,640 

16 

11 

" 

" 

«« 

65 

320 

32 

10 

3.974 

20,160 

19 

4 

" 

" 

<• 

66 

360 

36 

10 

4-471 

22,680 

21 

9 

«« 

" 

•  ' 

67 

400 

40 

10 

4,968     25,200 

24 

2 

'« 

" 

" 

68 

440 

44 

10 

5,465     27,720 

26 

7 

n 

" 

<< 

69 

480 

48 

10 

5,962     30,240 

29 

0 

" 

" 

■  1 

70 

5  2° 

52 

10 

6,458     32,760 

3i 

5 

1  i 

" 

>< 

7i 

'560 

56 

10 

6,955     35.28o 

33 

10 

" 

" 

t  ( 

72 

600 

60 

10 

7,452    37.800 

36 

3 

*  t 

" 

•  < 

73 

640 

64 

10 

7.949 

40,320 

38 

8 

•« 

'< 

<< 

74 

680 

68 

10 

8,446 

42,840 

41 

1 

1 1 

•' 

•  < 

75 

396 

36 

11 

4,9i5 

24,949 

21 

9 

7     io* 

IO       2\ 

12       6 

76 

440 

40 

11 

5,46i 

27,720 

24 

2 

1  < 

" 

" 

77 

484 

44 

11 

6,008 

30,497 

26 

7 

»i 

" 

" 

78 

528 

48 

1 1 

6,554 

33.268 

29 

0 

" 

" 

<< 

79 

572 

52 

11 

7,101 

36,045 

31 

5 

" 

" 

■  • 

80 

616 

56 

11 

7,646 

38,811 

33 

10 

" 

" 

*  1 

81 

660 

60 

11 

8,i93 

41,588 

36 

3 

" 

" 

" 

82 

704 

64 

11 

8,739 

44,359 

38 

8 

•' 

" 

<  i 

83 

748 

68 

11 

9,286 

47,^6 

41 

1 

*' 

" 

« 

84 

792 

72 

11 

9,832 

49.907 

43 

6 

" 

ru 

• 

85 

836 

76 

11 

10,379 

52,684 

45 

11 

1 1 

tt 

" 

86 

880 

So 

11 

10,925 

55,455 

4S 

4 

' 

" 

" 

87 

528 

44 

12 

6,549 

33,262 

26 

7 

8       6* 

IO        2j 

12     6 

88 

576 

48 

12 

7,145 

36,289 

2Q 

0 

( t 

" 

" 

89 

624 

52 

12  • 

7.741 

39,3J  7  , 

3i 

5 

" 

" 

" 

90 

672 

56 

12 

8,337 

42,344 

33 

10 

" 

" 

" 

91 

720 

60 

12 

8,933 

45,37i 

36 

3 

" 

" 

" 

92 

768 

64 

12 

9,529 

48,398 

38 

8 

1  < 

" 

" 

93 

816 

68 

12 

10,125 

5J,425 

41 

1 

" 

" 

•  • 

94 

864 

72 

12 

10,721 

54.452 

43 

6 

" 

" 

" 

95 

QT2 

76 

12 

1  1,317 

57.479 

45 

11 

" 

il 

" 

96 

960 

80 

12 

11,913 

60, 506 

48 

4 

<  < 

1  1 

•  < 

97 

IO08 

84 

12 

12,489    63,432 

5° 

9 

1 1 

" 

1 1 

98 

IO56 

88     i 

12 

13,065    66,357  : 

53 

2 

1 1 

(  ( 

•  • 

4io 


APPENDIX. 
LOGARITHMS. 


Nat. 

Proportional  Parts. 

Nos. 

0 

1 

2 

3 

4 

5 

6 

7 

8 

9 

0000 

0043 

0086 

0128 

1  2 

3 

4 

5  6 

7 

8  9 

10 

0170 

0212 

0253 

0294 

0334|0374 

4  8 

12 

17 

21  25 

29 

33  37 

11 

0414 

0453 

0492 

0531 

0569 

0607 

0645 

0682 

0719,0755 

4  8 

II 

15 

19  23 

26 

3°  34 

12 

0792 

0828 

0864 

0899 

0934 

0969 

1004 

1038 

1072  1 106 

3  7 

It 

*4 

17  21 

'-'4 

28  31 

13 

"39 

"73 

1206 

1239 

1271 

1303 

1335 

1367 

1399  1430 

3  6 

10 

13 

16  19 

23 

26  29 

14 

1461 

[492 

1523 

1553 

1584 

1614 

1644 

1673 

1703,1732 

3  6 

9 

12 

15  18 

21 

24  27 

15 

1 761 

1790 

1818 

1847 

1875 

1903 

1931 

1959 

1987  2014 

3  6 

8 

11 

14  17 

20 

22  25 

16 

2041 

2068 

2095 

2122 

2148 

2175 

2201 

2227 

22532279 

3  5 

S 

1 1 

13  16 

IS 

21  24 

17 

2304 

2330 

2355 

23S0 

2405 

2430 

2455 

2480 

2504 

2529 

2  5 

7 

10 

12  15 

17 

20  22 

18 

2553 

2577 

2601 

2625 

2648 

2672 

2695 

2718 

2742 

2765 

2  5 

7 

9 

12  14 

16 

19  21 

19 

2788 

2810 

2833 

2856 

2878 

2900 

2923 

2945 

2967 

2989 

2  4 

7 

9 

11  13 

16 

18  20 

20 

3010 

3032 

3054 

3075 

3096 

3"8 

3139 

3160 

3181 

3201 

2  4 

6 

8 

11  13 

'5 

17  19 

21 

3222 

3243 

3263 

3284 

3304 

3324 

3345 

3365 

3385 

3404 

2  4 

6 

8 

10  12 

'4 

16  18 

22 

3424 

3444 

3464 

3483 

3502 

3522 

3541 

356o 

3579 

3598 

2  4 

6 

8 

10  12 

14 

15  17 

23 

3617 

3636 

3655 

3674 

3692 

37" 

3729 

3747 

3766 

3784 

2  4 

6 

7 

9  " 

13 

15  17 

24 

3802 

3820 

3838 

3856 

3874 

3892 

39°9 

3927 

3945 

3962 

2  4 

5 

7 

9  " 

12 

14  16 

25 

3979 

3997 

4014 

4031 

4048 

4065 

4082 

4099 

4116 

4133 

2  3 

E 

7 

9  10 

12 

14  15 

26 

4150 

4166 

4183 

4200 

4216 

4232 

4249 

4265 

4281  4298 

2  3 

5 

7 

8  10 

1 1 

13  15 

27 

4314 

4330 

4346 

4362 

4378 

4393 

4409 

4425 

44404456 

2  3 

5 

6 

8  9 

1 1 

13  14 

28 

4472 

4487 

4502 

45i8 

4533 

4548 

4504 

4579 

45944609 

2  3 

5 

6 

8  9 

1  i 

12  14 

29 

4624 
4771 

4639 

4654  4669 

4683 

4698 

4713 

4728 

474214757 

1  3 

4 

6 

7  9 

IO 

12  13 

30 

4786 

4800  4814 

4829 

4843 

4857 

4871 

4886  4900 

1  3 

4 

6 

7  9 

10 

11  13 

31 

4914 

4928 

494214955 

4969 

4983 

4997 

501 1 

5024  5038 

1  3 

4 

6 

7  8 

IO 

11  12 

32 

5051 

5065 

5079(5092 

5105 

5"9 

5132 

5145 

5i59  5t72 

1  3 

4 

5 

7  8 

9 

11  12 

33 

5185 

5198 

5211 

5224 

5237 

5250 

5263 

5276 

5289  5302 

1  3 

4 

5 

6  8 

9 

IO  12 

34 

5315 

5328 

5340 

5353 

5366 

5378 

5391 

5403 

54i6 

5428 

1  3 

4 

5 

6  8 

9 

IO  II 

35 

5441 

5453 

5465 

5478 

5490 

5502 

5514 

5527 

5539 

555i 

I  2 

4 

5 

6  7 

9 

IO  II 

36 

5563 

5575 

5587 

5599 

5611 

5623 

5635 

5647 

5658 

5670 

I  2 

4 

5 

6  7 

8 

IO  II 

37 

5682 

5694 

5705 

571? 

5729 

5740 

5752 

5763 

5775 

5786 

1  2 

3 

5 

6  7 

8 

9  10 

38 

5798 

5809 

5821 

5832 

5843 

5855 

5866 

5877 

5888 

5899 

1  2 

3 

5 

6  7 

8 

9  IO 

39 

5911 

5922 

5933 

5944 

5955 

5966 

5977 

5988 

5999 

6010 

1  2 

3 

4 

5  7 

8 

9  IO 

40 

6021 

6031 

6042 

6053 

6064 

6075 

6085 

6096 

6107 

6117 

1  2 

3 

4 

5  6 

8 

9  IO 

41 

6128 

6138 

6149 

6160 

6170 

6180 

6191 

6201 

6212 

6222 

1  2 

3 

4 

5  6 

7 

8  9 

42 

6232 

6243 

6253 

6263 

6274 

6284 

6294 

6304 

6314 

6325 

1  2 

3 

4 

5  6 

7 

8  9 

43 

6335 

6345 

6355 

6365 

6375 

6385 

6395 

6405 

6415 

6425 

1  2 

3 

4 

5  6 

7 

8  9 

44 

6435 

6444 

6454 

6464 

6474 

6484 

6493 

6503 

6513 

6522 

1  2 

3 

4 

5  6 

7 

8  9 

45 

6532 

6542 

6551 

6561 

6571 

6580 

6590 

6599 

6609 

6618 

I  2 

3 

4 

5  6 

7 

8  9 

46 

6628 

6637 

6646 

6656 

6665 

6675 

6684 

6693 

6702 

6712 

I  2 

3 

4 

5  6 

7 

7  8 

47 

6721 

6730 

6739 

6749 

6758 

6767 

6776 

6785 

6794 

6803 

I  2 

3 

4 

5  5 

6 

7  8 

48 

6812 

6821 

6830 

6839 

6848 

6857 

6866 

6875 

6884 

6893 

I  2 

3 

4 

4  5 

6 

7  8 

49 

6902 

691 1 

6920 

6928 

6937 

6946 

6955 

6964 

6972 

6981 

I  2 

3 

4 

4  5 

6 
6 

7  8 

50 

6990 

6998 

7007 

7016 

7024 

7033 

7042 

7050 

7059 

7067 

I  2 

3 

3 

4  5 

7  8 

51 

7076 

7084 

7093 

7101 

7110 

7118 

7126 

7135 

7143 

7152 

I  2 

3 

3 

4  5 

6 

7  8 

52 

7160 

7168 

7177 

7185 

7193 

7202 

7210 

7218 

7226 

7235 

I  2 

2 

3 

4  5 

6 

7  7 

53 

7243 

7251 

7259 

7267 

7275 

7284 

7292 

7300 

73o8 

7316 

I  2 

2 

3 

4  5 

6 

6  7 

54  7324  7332  7340 

7348 

7356 

7364  7372 

738o 

7388 

7396 

I  2 

2 

3 

4   5 

6 

6  7 

APPENDIX. 
LOGARITHMS. 


411 


Nat. 
Nos. 


55 
56 
57 
68 
59 

60 
61 
62 
63 
64 

65 
66 
67 

68 
69 


7404 
7482 
7559 
7634 


77'")  77 


7782 

7853 
7924 

7993 
8062 


7412 
7490 
7566 
7642 
16 


7789 
7860 

793i 
8000 


8261 

8325 
8388 

70  845' 

71  i85'3 


8129  8136 
8195  8202 


8573 
8633 
8692 


8751 


72 
73 
74 

75 
76 

77  8865 

78  S921 

79  S976 

80  9031 

81  90S:; 

82  913S 

83  9191 

84  '9243 


85  9294 

86  9345 

87  9395 

88  J9445 

89  9494 

90  J954 

91  9590 

92  I96  " 
93 
94  973 


95 
96 
97 
98 
99 


9777 
9823 


9912 
9956 


8267 
8331 
8395 

8457 
8519 

8579 
8639 
S69S 


8756 
8814 


7419 
7497 
7574 
7649 

7723 

7796 
7868 
7938 
8007 
8075 


814 

8209 

8274 

8338 

8401 

8463 
8525 
8585 
8645 
8704 


7427 
7505 
7582 

7657 
773i 
7803 
7875 
7945 
8014 
8082 


8149 
8215 


8280  8287 


8344 
8407 


8470  8476 


8531 
8591 
8651 
8710 


87628768 
8820882s 
8876,8882 
3927J8932I8938 
8982J8987J8993 

9036  9042  9047 
9090  9096  gio'i 


9M3 
9196 
9248 


9299 
9350 
9400 
9450 
9499 


91499154 

9201  9206 
9253925S 


9304  9309 
93559300 
9405  9410 

94  5^  946o 
9504  9509 


9547  9552,9557 
9595  9600J9605 
9643  9647 '9652 
9689  9694  9699 
973697419745 


9782 

9827 
9872 

9917 


97S6;979i 
9832,98361984 
9877J9SS1 
9921  992619930 


9961 19965  9969 


7435 
7513 
7589 
7664 
7738 

7810 

7882 
7952 
8021 


8156 
8222 


8351 
8414 


8537 
8597 
8657 
8716 


8774 
8831 
8887 
8943 


9053 
9106 

9159 
9212 
9263 


9315 
9365 
94i5 
9465 
9513 
9562 


74437451 
7520I7528 
7597!76o4 
7672)7679 

7745  7752 

7818J7825 
7889 

79597966 
8o28|8o35 
8096  8102  8109 


8162 

8228 
8293 

8357 
8420 

8482 

8543 
8603 
8663 
8722 


8169 

8235 
8299 

8363 
8426 

8488 

8549 
S609 


8727 


87798785 
88378842 


8949^954 
9U04 

9058J9063 
9112911 

916591 

9217  9222 
92699274 


9320 
937o 
9420 
9469 
95i8 

9566 


9609J9614 
96579661 
9703J970S 

509754 


9795 
1 
9886 


9974 


9800 

9845 
9890 

9934 
9978 


9325 
9375 
9425 
9474 
9523 

9571 
9619 
9666 
9713 


9805 
9850 
9894 


7459 
7536 
7612 
7686 
776o 

7832 
7903 
7973 
8041 


8176 
8241 
8306 
8370 
8432 

8494 

8555 
8615 

8675 
8733 


8791 


8904 

S960 

wggois 

9069 

122 

175 

9227 

9279 


79i 


7466 

7543 
7619 
7694 
7767 

7839 
7910 

798o 
8048 
81 16 


8182 
8248 
8312 
8376 
8439 

8500 
8^61 
8621 
1 
8739 


8797 
8854 
8910 
8965 
9020 

9074 
9128 
9180 
9232 
9284 


7474 
7551 
7627 
7701 
7774 
7846 
79'7 
7987 
8055 
8122 


Proportional  Parts. 


8189 

8254 

8319 
8382 

8445 
8506 
8567 
8627 


8745 


9330  9335 
9380J9385 

9430J9435 
94799484 
95289533 

95769581 
9624  9628 
9671  9675 
97179722 
9759  976319768 


8802 
8859 
8915 
8971 
9025 
9079 

9133 
9186 
9238 
9289 


9340 
9390 
9440 
9489 
9538 
9586 

9633 
9680 

9727 
9773 


9809  9814 

98549859 

9S999903 

9939  9943  994S  9952 

9983  9987  9991:9996 


9818 
9863 
990S 


1234     5    67     8    9 


2  2 
2  2 
2  2 
1  2 
1  2 

1  2 
1  2 
1  2 
1  2 
1  2 


1  2 
1  2 
1  2 
1  2 

1  2 

1  2 
1  2 
1  2 
1  2 
1  2 


4  5 

4  5 

4  5 

4  4 

4  4 

4  4 

4  4 

3  4 

3  4 

3  4 


3  4 

3  4 

3  3 

3  3 

3  3 

3    3 
3|  3 
3 
3 
3 


Oil 

o  1   1 

Oil 
O  I  I 
O    I     I 


3    3 


4  4 

4  4 

4  4 

31  4  4 

3    4  4 


4  4 

4  4 

4  4 

4  4 

3  4 


412  APPENDIX. 

Explanation  of  the  Table  for  Finding  the  Area  of 
Segment  of  a  Circle. — The  areas  given  in  the  table  are  for 
a  circle  I  inch  in  diameter.  The  diameter  is  divided  into 
1000  parts,  and  the  area  for  segments  of  different  heights  can 
be  taken  directly  from  the  table,  since  the  ratio  of  the  height 
of  the  segment  to  the  diameter  of  the  circle  is  the  same  as 
the  height  of  the  segment. 

For  a  circle  whose  diameter  is  other  than  unity.  Given 
the  diameter  of  the  circle  and  the  height  of  segment.  Re- 
quired area  of  segment.  Divide  height  of  segment  by  diameter; 
find  area  given  in  the  table  opposite  this  ratio ;  multiply  this 
area  by  the  square  of  the  diameter  and  the  result  is  the  re- 
quired area. 

Example. — Dia.  of  circle  =  60",  height  of  segment  =  18". 

1 8  -7-  60  =  .  30 ;  area  in  table  opposite  .30  is  .19817. 
.19817  X  60  X  60  =  area  of  segment  =  713.4  sq.  in. 

Given  the  diameter  of  the  circle  and  the  area  of  a  segment, 
to  find  the  height. 

Divide  the  area  of  the  segment  by  the  square  of  the  diam- 
eter. Find  in  the  table  the  area  nearest  to  this,  multiply 
the  ratio  corresponding  to  this  by  the  diameter  of  the  circle, 
and  the  result  is  the  required  height  of  the  segment. 

Example. — Area  of  segment  =  713.4  sq.  in. 

Diameter  of  circle  =  60".  Required  the  height  of  the 
segment. 

— - — '——  =  .10817.    Ratio  opposite  this  is  .300. 
60  X  60  y     '  *^ 

.300  X  60'    =   18",  the  required   height. 

Example  — Area  of  segment  =  640  sq.  in. 
Diameter  of  circle  =  50". 

640  .  .  . 
=.2;6o;  nearest  ratio,  .302. 

50X50 

.362  X  50  =   18.10",  the  required  height. 


APPENDIX.  413 

TABLE   FOR    FINDING    AREAS    OF   SEGMENTS   OF   A    CIRCLE. 


—  0  l> 

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•32095 

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•13562 

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.17912 

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•22509 

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.22603 

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.22792 

2 

.27580 

2 

■32491 

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3 

.18272 

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.22886 

3 

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■  32500 

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.13984 

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.22980 

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•27775 

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■  8542 

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.27969 

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7 

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8 

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8 

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9 

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9 

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.290 

.18905 

.340 

•23547 

.390 

•28359 

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1 

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.295 

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6 

■  1 5°°9 

6 

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6 

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6 

■28945 

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7 

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7 

.24212 

7 

.29043 

7 

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8 

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8 

.19634 

8 

•24307 

8 

.29141 

8 

•  34079 

9 

.15268 

9 

.19725 

9 

.24403 

9 

.29239 

9 

•34179 

.250 

•'5355 

.300 

.19817 

•35o 

.24498 

.400 

■29337 

.450 

.34278 

1 

.15441 

1 

.19908 

1 

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1 

•29435 

1 

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2 

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2 

.20000 

2 

. 24689 

2 

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2 

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3 

■15615 

3 

.20092 

3 

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3 

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3 

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4 

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4 

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.15789 

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6 

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6 

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6 

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6 

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7 

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7 

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7 

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7 

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7 

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8 

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8 

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8 

25263 

8 

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8 

3?o75 

9 

.16139 

9 

.20645 

9 

■25359 

9 

. 30220 

9 

•35!75 

4M 


APPENDIX 


NATURAL   TRIGONOMETRIC 
FUNCTIONS. 


CIRCLES 


Deg. 

Sine. 

Tangent. 

Cot. 

1 

Cos. 

Deg. 

o 

.OOOO 

.OOOO 

.  Infinite 

I.  OOOO 

90 

i 

•OI75 

•0175 

i  57  290 

.9998 

89 

2 

■0349 

•0349 

28.636 

•9994 

88 

3 

0523 

.0524 

19.081 

.9986 

87 

4 

,0698 

.0699 

14.301 

.9976 

86 

5 

.0872 

.0875 

11.430 

.9962 

85 

6 

.1045 

.IO5I 

9-5144 

•9945 

84 

7 

.1219 

.1228 

8.1443 

•9925 

83 

8 

.1392 

.1405 

7.II54 

■9903 

82 

9 

.1564 

.1584 

63138 

•9S77 

81 

IO 

•  I736 

•1763 

5-67I3 

.9848 

80 

ii 

.1908 

.1944 

5.1446 

.9816 

79 

12 

.2079 

.2126 

4.7046 

.9781 

78 

13 

.2250 

.2309 

4.3315 

•  9744 

77 

J  4 

.2419 

•2493 

4.0108 

.9703 

76 

IS 

.2588 

.2679 

3-7321 

•9659 

75 

1 6 

.2756 

.2867 

3.4874 

.9613 

74 

17 

.2924 

•3057 

3.2709 

•9563 

73 

18 

.3090 

•3249 

3-0777 

■  95" 

72 

19 

.3256 

•3443 

2.9042 

•9455 

7i 

20 

.3420 

.3640 

2-7475 

•9397 

70 

21 

.3584 

•3839 

2.6051 

.9336 

69 

22 

•  3746 

.4040 

2.4751 

.9272 

68 

23 

•  3907 

.4245 

2-3559 

.9205 

67 

24 

.4067 

•4452 

2.2460 

•9'35 

66 

25 

.4226 

.4663 

2.1445 

.9063 

65 

26 

•4384 

•4877 

2..0503 

.8988 

64 

27 

.4540 

•5095 

1.9626 

.8910 

63 

23 

•4695 

■5317 

1.8807 

.8829 

62 

29 

.4848 

•5543 

1  8040 

.8746 

61 

30 

.5000 

•5774 

I-732I 

.8660 

60 

31 

.5150 

.  6009 

1.6643 

.8572 

59 

32 

.5299 

6249 

1.6003 

.8480 

58 

33 

.5446 

.6494 

1-5399 

.8387 

57 

34 

•5592 

•6745 

1.4826 

.8290 

56 

35 

•573*3 

.7002 

1.4281 

.8192 

55 

36 

•587S 

.7265 

I-3764 

.8090 

54 

37 

.6018 

■7536 

1.3270 

.7986 

53 

38 

•6i57 

•7813 

1.2799 

.7880 

52 

39 

.6293 

.8098 

1  •  2349 

•7771 

51 

40 

.6428 

8391 

1.1918 

.7660 

50 

41 

.6561 

.S693 

1-1504 

•7547 

49 

42 

.6691 

.9004 

1 . 1 1 06 

•7431 

48 

43 

.6820 

•9325 

1.0724 

■7314 

47 

44 

.6947 

•9b57 

1-0355 

•7193 

46 

45 

.7071 

I.  OOOO 
Cot. 

I. OOOO 
Tangent. 

.7071 
Sine. 

45 

Deg. 

Ccs. 

Deg. 

Diam. 
Inches. 


Circumf. )  Area, 
Inches.  1  Sq.  In. 


12 

37f 

"3s 

14 

44 

154 

16 

5oi 

201 

18 

•   56£ 

254^ 

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3'4* 

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163I 

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169I 

2  290  \ 

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182^ 

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3'4£ 

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32of 

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APPENDIX. 
ROUND    RODS    OF   WROUGHT   IRON. 


415 


Weight 

Diameter 

Diameter 

Excess  of 

Diameter 

Circumfer- 

Area in 

of  Rod 

of  Upset 

of  Screw 

Threads 

Area  of 

in  Inches. 

ence 

Sq.  Inches. 

One  Foot 

Screw- 

at  Root  of 

per  Inch 

ScrewEod 

in  Inches. 

Long. 

End. 
Inches. 

Thread. 
Inches. 

Number. 

over  Bar. 
Per  Cent. 

0 

1/16 

.1963 

.OO31 

.010 

1/8 

.3927 

.0123 

.041 

3/i6 

•589O 

.0276 

.092 

i/4 

.7854 

.0491 

.  164 

5/i6 

.9817 

.0767 

.256 

3/8 

I.1781 

.  1 104 

.368 

7/16 

1-3744 

.1503 

.501 

1/2 

1.5708 

.1963 

.654 

3 

1 

.620 

IO 

6* 

9/16 

1 . 7671 

.24S5 

.828 

f 

.620 

IO 

21 

5/8 

I-9635 

.3068 

I.023 

7 
TS 

•731 

9 

57 

11/16 

2.1598 

■3712 

1.237 

I 

.837 

8 

48 

3/4 

2.3562 

.4418 

1-473 

I 

.837 

8 

25 

13/16 

2.5525 

•5185 

1.728 

i£ 

.940 

7 

34 

7/8 

2.7489 

.6013 

2.004 

*i 

I.065 

7 

48 

I5/I6 

2-9452 

.6903 

2.301 

4 

I  .065 

7 

29 

1 

3.1416 

•7854 

2.618 

it 

1. 160 

6 

35 

1/16 

3-3379 

.8866 

2-955 

it 

I.  160 

6 

19 

1/8 

3-5343 

.99-10 

3-313 

4 

I.284 

6 

30 

3/i6 

3-7306 

1. 1075 

3.692 

n 

I.2S4 

6 

17 

1/4 

3.9270 

1.2272 

4.091 

it 

I.389 

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23 

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if 

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5.410 

if 

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5 

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5-io5i 

2.0739 

6.913 

2£ 

1-837 

4^ 

28 

3/4 

5-4978 

2.4053 

8.018 

2i 

I.962 

4* 

26 

7/8 

5.8905 

2.7612 

9.204 

2| 

2.0S7 

4* 

24 

2 

6.2832 

3-I4I6 

10.47 

2| 

2.175 

4 

18 

1/8 

6.6759 

3.5466 

11.82 

2| 

2.300 

4 

17 

i/4 

7.0686 

3-976I 

13-25 

1" 

2.550 

4 

28 

3/8 

7-46I3 

4.4301 

M-77 

3 

2.629 

J5 

23 

1/2 

7-8540 

4.9087 

16.36 

3i 

2-754 

3i 

21 

5/8 

8.2467 

5-4II9 

18.04 

3i 

2.879 

3i 

20 

3/4 

8.6394 

5-9396 

19.  So 

31 

3.OO4 

3* 

19 

7/8 

9.0321 

6.4918 

21.64 

3i 

3  225 

3i 

26 

3 

9.4248 

7.0686 

23.56 

3f 

3-317 

3 

22 

4i6 


APPENDIX. 
LAP-WELDED    BOILER-TUBES. 


, 

rt -3' 

?i    • 

—    X 

,~  c 

j    £ 

w  u 

U 

U 

V 

K  ^ 

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S3 

a.  <* 

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^ 

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ii 

1 1 

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12 

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37-7° 

36 

26 

1 13.10 

104.63 

•32 

•33 

3-  '4 

3.O2 

28.46 

SCREW-THREADS. 
Angle  of  thread  6o\     Flat  at  top  and  bottom  —  |  of  pitch. 


Diameter  of 

Diameter  at 

Threads 

! 

Diameter  of 

Diameter  at 

Threads 

Screw. 

Root  of  Thread, 

per  Inch, 

Screw. 

Root  of  Thread, 

per  Inch, 

Inches. 

Inches. 

No. 

Inches. 

Inches. 

No. 

Ya 

.185 

20 

1 

2 

1 .712 

44 

R 

.240 

18 

2>4 

1 .962 

44 

% 

•294 

16 

24 

2.175 

4 

IS 

•344 

M 

2*i 

2425 

4 

4 

.400 

•3 

3 

2.629 

3\§ 

,\ 

•454 

12 

3^4 

2.879 

34 

% 

.507 

11 

3V3 

3.100 

M 

Yx 

.620 

10 

zY* 

3-3'7 

3 

% 

•731 

9 

4 

3-5°7 

3„, 

t 

•837 

3 

4Vi 

3-798 

2% 

iH 

.940 

7 

44 

4.028 

*K 

■  ^ 

1  065 

7 

4% 

4  255 

1% 

i« 

1 .  160 

6 

5 

4.480 

24 

14 

1   284 

6 

5^ 

4-730 

24 

>&f 

1.389 

54 

54 

5  053 

2% 

'H 

1   490 

5 

5H 

5-203 

2% 

.74 

1 .615 

5 

6 

5423 

2>4 

APPENDIX.  417 

WROUGHT-IRON    WELDED    STEAM-,    GAS-,    AND    WATER-PIPE. 


3iameter. 

Transverse  Areas. 

Nominal 

Number  of 

Weight 

per 

Foot. 

Threads 
per  Inch  of 

Nominal 

Actual 

Actual 

Thickness. 

External. 

Internal. 

Internal 

External. 

Internal. 

Inches. 

Inches. 

Indies. 

Inches. 

Sq.  In. 

Sq.  In. 

Pounds. 

% 

.405 

.27 

.068 

.129 

•0573 

.241 

27 

H 

.543 

•364 

.088 

.229 

.1041 

■42 

18 

5g 

.675 

•494 

.091 

.358 

.1917 

.559 

.8 

\% 

.84 

.623 

.109 

•554 

.3048 

.837 

>4 

H 

1.05 

.824 

.113 

.866 

•5333 

1. US 

li 

1 

•^S 

1 .048 

•'34 

1.358 

.8626 

1.668 

»« 

*H 

1.66 

1.38 

•  14 

a  164 

1.496 

2.244 

"H 

tH 

1.9 

1 .61 1 

.145 

2.835 

2.038 

2.678 

"« 

2 

2  375 

2.067 

•IS4 

4-43 

3-356 

3.609 

11^ 

*H 

2.875 

2.468 

.204 

6.492 

4-784 

5-739 

8 

3 

3  5 

3.067 

.217 

9.621 

7.388 

7-53t> 

8 

3H 

4- 

3-548 

.226 

12.566 

9.887 

9.001 

8 

4 

4-5 

4.026 

■2*7 

15.904 

"•73 

10.665 

8 

4^ 

5- 

4.508 

.240 

19.635 

15.961 

12.34 

8 

5 

5  563 

5 -°45 

•2  59 

24.306 

19.99 

14.502 

8 

6 

6.625 

6.065 

.28 

34-472 

28.888 

18.762 

8 

7 

7-625 

7.023 

.301 

45.664 

38.738 

23.271 

8 

3 

8.625 

7.982 

.322 

58.426 

50.04 

28.177 

8 

9 

9.625 

8.937 

•344 

72.76 

62.73 

33.701 

8 

10 

10.75 

10.019 

•3% 

90.763 

78.839 

40.065 

8 

11 

12 

11.25 

•375 

113.098 

99 ■ 402 

45-95 

8 

12 

12.75 

12 

•375 

127.677 

113.098 

48.985 

8 

'3 

>4 

13.25 

•375 

!53-938 

137.887 

53-921 

8 

14 

15 

14.25 

•375 

176.715 

I59-485 

57-893 

8 

15 

16 

15.25 

•375 

201 .062 

182  655 

61.77 

8 

18 

17.25 
19.25 

21 .25 

254-47 
314. 16 
380.134 

233.706 
291 .04 
354  657 
424.558 

69.66 
77-57 
85.47 

20 

22 

•375 

•375 

24 

23-2:> 

•375 

452  39 

93-37 

WROUGHT-IRON'    WELDED    EXTRA    STRONG    PIPE. 


% 

.405 

205 

.1 

.129 

•°33 

.29 

27 

Y\ 

■54 

294 

.123 

.229 

.068 

■54 

18 

% 

•675 

421 

.127 

•358 

.139 

•74 

18 

% 

.84 

542 

.149 

•554 

.231 

1 .09 

»4 

H 

1.05 

736 

•  157 

.866 

•452 

1.39 

14 

1 

'•3'5 

951 

.182 

1-358 

•7' 

2.17 

11^ 

>H 

1.66              1 

272 

.194 

2.164 

1 .271 

3 

itH 

1^ 

1.9                1 

494 

.203 

2.835 

1-753 

363 

"^ 

2 

2-375             1 

933 

.221 

4-43 

2-935 

5  02 

"H 

2^ 

2  875             2 

3'5 

.28 

6.492 

4.209 

y.67 

8 

3 

3-5                 2 

892 

.304 

9.621 

6.569 

10.25 

8 

M 

4                     3 

358 

•321 

12.566 

3.856 

12.47 

8 

4 

4-5                3 

818 

•  341 

I5-904 

11.449 

M-97 

8 

5 

5-563            4 
6.625            5 

8i3 

•375 

24.306 

18.193 

20.54 

8 

6 

75 

•437 

34.472 

25.967 

28.58 

8 

4i8 


APPENDIX. 


HEAT  OF  THE  LIQUID. 


• 

0 

0' 

0- 

• 

0 ' 

fa 

m 

fa 

JJ, 

fa* 

"5 

fa 

" 

fa' 

« ! 

fa" 

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o 

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0 

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0 

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0 

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0 

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0 

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c  a  > 

C  3  > 

0  3  > 

c  3  > 

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d 

^  CfO 

d 

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d 

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d 

~  erg 

d 

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d 

| 

6 

a 
9 

0,-h  03 

i 

V 

_  —  03 

E 

=  •"-£: 

Oy—    0! 

i 

H 

B 

H 

X 

H 

X 

f- 

X 

H 

X 

H 

X 

32 

0 .0 

76 

44- I 

121 

89.0 

166 

1340 

211 

179.3 

256 

224.9 

33 

1 .0 

77 

45.1 

122 

90.0 

167 

1350 

212 

180    3 

257 

225.9 

34 

2 .0 

78 

46.  I 

123 

91 .0 

168 

136.0 

213 

181.3 

258 

226    9 

35 

3° 

79 

47-1 

124 

92  .0 

169 

1370 

214 

182.3 

259 

227.9 

36 

4.0 

80 

48.I 

125 

93    0 

170 

1380 

215 

183.3 

260 

229. c 

37 

So 

81 

49- I 

126 

94.0 

171 

1390 

216 

184.3 

261 

230.0 

38 

6.1 

82 

SO.I 

127 

95-0 

172 

140.0 

217 

185.3 

1   262 

231 .0 

39 

7-1 

83 

51. I 

128 

96.0 

173 

141 .0 

218 

186.3 

263 

232.0 

40 

8   1 

84 

52.1 

129 

97   0 

174 

142  .0 

219 

187.4 

264 

2330 

41 

9.1 

85 

53- 1 

130 

98.0 

175 

1430 

220 

188.4 

265 

234    0 

42 

10. 1 

86 

54.1 

131 

99.0 

176 

144-0 

221 

189.4 

266 

2350 

43 

11 . 1 

87 

55-1 

132 

100  .0 

177 

I45-0 

222 

190.4 

267 

236.1 

44 

12  . 1 

88 

56.1 

133 

101 .0 

178 

146.0 

223 

I9I-4 

268 

237.1 

45 

131 

89 

57-1 

134 

102  .0 

179 

I47-0 

224 

192.4 

269 

238.I 

46 

14. 1 

90 

58.1 

135 

103.0 

180 

148.0 

225 

193-4 

270 

230.  I 

47 

15. 1 

91 

59-1 

136 

104  0 

181 

I49.0 

226 

194-4 

271 

240.  2 

48 

16. 1 

92 

60. 1 

137 

105. 0 

182 

150. I 

227 

195.4 

272 

241  .  2 

49 

17. 1 

93 

61. 1 

138 

106  .0 

183 

151 -I    1 

228 

196.5 

273 

242  .2 

50 

18. 1 

94 

62  .1 

139 

107  .0 

184 

152  . 1 

229 

I97-S 

274 

243-2 

51 

19. 1 

95 

63- 1 

140 

108.0 

185 

1 53- 1 

230 

198.5 

275 

244.2 

52 

20. 1 

96 

64. 1 

141 

109  .0 

186 

154. 1 

231 

199-5 

276 

245-3 

53 

21 . 1 

97 

65.0 

142 

1 10.0 

187 

IS5-I    | 

232 

200.5 

277 

246.3 

54 

22  . 1 

98 

66.0 

143 

III  .0 

188 

156. 1 

233 

20T  .5 

278 

247.3 

55 

23-1 

99 

67  .0 

144 

112  .O 

189 

157.  1 

234 

202  .5 

279 

248.3 

56 

24.1 

100 

68.0 

145 

1I3.0 

190 

158.1 

235 

203.6 

280 

249.4 

57 

25.1 

IOI 

69.0 

146 

114.0 

191 

159. 1 

236 

204.6 

1   281 

250.4 

58 

26.1 

102 

70.0 

147 

IIS.O 

192 

160.  1 

237 

205  .6 

282 

251  -4 

59 

27.1 

103 

71.0 

148 

Il6. O 

193 

161. 1 

238 

206 . 6 

283 

2524 

60 

28.1 

104 

72  .0 

149 

I  17  .O 

194 

162  .  1 

239 

207  .6 

284 

253-4 

61 

29.1 

105 

73-0 

150 

Il8. O 

195 

1 63. 1 

240 

208.6 

285 

2S4-5 

62 

30.1 

106 

74-0 

151 

I  19  .0 

196 

j  64 . 1 

241 

209 . 6 

286 

255    5 

63 

31  I 

107 

7S-0 

152 

120.0 

197 

165. 1 

242 

210.  7 

287 

2565 

64 

32.1 

108 

76.0 

153 

121  .O 

198 

166 . 2 

243 

211 .7 

288 

257-5 

65 

331 

109 

77.o 

154 

I22.0 

199 

167.2 

244 

212.7 

289 

258  6 

66 

34.1 

no 

78.0 

155 

123     O 

200 

168.2 

245 

2137 

290 

259.6 

67 

351 

III 

790 

156 

I24.0 

201 

169 . 2 

246 

214.7 

291 

260. 6 

68 

36.1 

112 

80.0 

157 

I25.0 

202 

170.2 

247 

215    7 

292 

261 .6 

69 

37.1 

113 

81.0 

158 

I26.O 

203 

171 .2 

248 

216.7 

293 

262    7 

70 

38.1 

114 

82.0 

159 

127  .O 

204 

172.2 

249 

2177 

294 

263.7 

7i 

391 

1.1 5 

83.0 

160 

I28.0 

205 

173-2 

250 

218.8 

295 

264.7 

72 

40.1 

116 

84.0 

161 

129  .O 

206 

174.2 

251 

219.8 

296 

265.7 

73 

41  I 

117 

85.0 

162 

I30.0 

207 

175-2 

252 

220 . 8 

297 

266.7 

74 

42. 1 

118 

86.0 

163 

I3IO 

208 

176.2 

253 

221.8 

298 

267   8 

75 

43- 1 

119 

87.0 

164 

132  .0 

209 

177.2 

254 

222  .8 

299 

268.8 

120 

88.0 

165 

133    O 

210 

178.3 

255 

223.8 

300 

269.8 

VOLUME  AND  WEIGHT  OF  DISTILLED  WATER. 


Temp. 

Weight  of  a 

Temp 

Weight  of  a 

Temp. 

Weight  of  a 

Degrees 

Cubic  Foot     1 

Degrees 

Cubic  Foot 

Degrees 

Cubic  Foot 

Fahr. 

in  Pounds. 

Fahr. 

in  Pounds. 

Fahr. 

in  Pounds. 

32 

62  .417 

90 

62  .  1 10 

160 

61  .007 

39    1 

62 .425 

100 

62 . 000 

170 

60   801 

40 

62.423 

I  iO 

61 .867 

180 

60.587 

50 

62.409 

120 

61 . 720 

190 

60.366 

60 

62.367 

130 

61 .556 

200 

60 . 136 

70 

62 . 302 

140 

61.388 

210 

59 . 894 

80 

62.218 

150 

61 . 204 

212 

59707 

APPENDIX. 
PROPERTIES  OF  SATURATED   STEAM. 


419 


Pressure 
Pounds 

per 
Square 

Temperature 
Degrees  F. 

Heat  of 

Liquid 
above  320. 

Heat  of 

Vap<  >rization 

or  Total  Latent 

Heat. 

Heat  Contents 
above 

at   32°  F. 

Volume  in 
Cubic  Feet 

of 
One  Pound. 

Inch. 

5 

162.3 

I303 

I OOO  O 

II30-3 

78.3 

10 

193 

2 

161. 3 

981 

4 

II42.7 

38.4 

15 

213 

0 

181. 3 

969 

1 

1 1  50   4 

26.3 

20 

227 

9 

196.4 

959 

4 

"55-8 

20. 1 

25 

240 

1 

208.  7 

95i 

4 

1 160. 1 

16.3 

30 

250 

3 

219.  I 

944 

4 

"63.5 

13  7 

35 

259 

3 

2  28.  2 

938 

2 

1166.4 

11. 9 

40 

267 

3 

236.4 

932 

6 

1 169.0 

105 

45 

2  74 

5 

243  -7 

927 

5 

1171 . 2 

9  39 

5° 

281 

0 

2504 

922 

8 

1173.2 

8.5r 

55 

287 

1 

256.6 

918 

4 

"75  0 

778 

60 

292 

7 

262.4 

914 

3 

1176.7 

7   17 

65 

298 

0 

267.8 

910 

4 

1 1 78. 2 

665 

70 

3°3 

0 

272.9 

906 

6 

"79-5 

6.  20 

75 

3°7 

6 

277.7 

903 

1 

1180.8 

581 

80 

312 

1 

282.  2 

899 

8 

1182.0 

5-47 

85 

316 

3 

286.5 

896 

6 

1183.1 

S-i6 

90 

320 

3 

200.  7 

893 

5 

1 184. 2 

489 

95 

324 

2 

294.6 

890 

5 

1185.1 

4.64 

100 

327 

9 

2985 

887 

6 

1 186. 1 

4-43 

i°5 

331 

4 

302.1 

884 

8 

1 186. 9 

4- 23 

no 

334 

8 

3°5  6 

882 

1 

1 187. 1 

405 

"5 

338 

1 

309.0 

879 

5 

1188.5 

3-88 

120 

34i 

3 

312.3 

876 

9 

1 189. 2 

3-72 

125 

344 

4 

315  5 

874 

5 

1 190.0 

358 

130 

347 

4 

318.6 

872 

1 

1 190. 7 

3-45 

135 

35° 

3 

321-5 

869 

8 

1191.3 

3-33 

140 

353 

1 

324  4 

867 

4 

1191 .8 

3.22 

145 

355 

8 

327-3 

865 

2 

1192.5 

3-12 

150 

358 

5 

33°  ° 

863 

0 

"93  0 

3-oi 

155 

361 

1 

3327 

860 

9 

1193.6 

2.92 

160 

363 

6 

335-3 

858 

8 

1 194. 1 

2.83 

16S 

366 

1 

337  9 

856 

8 

1 194. 7 

2-75 

170 

368 

5 

340  4 

854 

8 

1 195. 2 

2.67 

175 

37o 

9 

342.8 

852 

8 

1195.6 

2.60 

180 

373 

2 

345  •  2 

850 

9 

1 196. 1 

2-53 

185 

375 

4 

347-5 

849 

0 

1 196. 5 

2-47 

190 

377 

6 

349  8 

847 

1 

HQ6.9 

2.41 

195 

379 

8 

3521 

845 

3 

1197.4 

2.36 

200 

381 

9 

354-3 

843 

5 

1197.8 

2.  29 

205 

384 

0 

356  4 

841 

7 

119S.1 

2.  24 

210 

386 

0 

358.6 

S40 

0 

1 198. 6 

2.18 

215 

388 

0 

360 . 6 

838 

3 

1198.9 

2. 14 

220 

390 

0 

362.7 

836 

6 

"99  3 

2.09 

225 

391 

9 

364-7 

834 

9 

1 199. 6 

2.04 

230 

393 

8 

^66.6 

833 

3 

1199.9 

2.00 

235 

395 

7 

368.6 

831 

7 

1200.3 

1 .96 

240 

397 

5 

370.5 

830 

1 

1 200 . 6 

1.92 

245 

399 

3 

372-4 

828 

5 

1200.9 

1.88 

250 

401 

1 

374-2 

826  9 

1 201 . 1 

185 

PLATE    L 


PLATE    L 


PLATE    II. 


FIC.  3 


CopjH-l    \Y 


FIC.  5 


FIC.  6 


PLATE   III. 


UJL-4 14^-  — 


17-1 1 


1 

J 


^ ^  """       . 

TT         JT~-  Oils', 


.  .GSE.ANDF. 
E.78J  F.    nOX'FRQM  BACK  ENO. 


■j-4 s  _  I 'I 

■j  -  JjHf- 


! 


•-B- 


_  A L i        ~— -  — -f'fc  *=-.  *=* 


-6 


_2}4  PLUG  FRONT  END 


:!RE  BOX     REAR  ELEVATION 


LOCOMOTIVE  BOILER 

160  LBS.  PRESSURE 


3t= 

SECTION  THROUGH  FIRE  BOX     REAR  ELEVATION 


PLATE  IV. 


SECTION  C-C  LOOKING  BACK 


SECTION  A-A  LOOKING  FRONT. 


SECTION  C-C  LOOKING  BACK 


SECTION  B-B  LOOKING  FRONT. 


PLATE   V. 


o 


1  '  '  '  '  '  '"i  i  m  i  i  i  i  i  i  i  "i  !  i  ii  i  i  i  )  i  i  m  i  i  I  :  1  i  ffi  i  i  I  i  i  i  i  r  :  i  j"   i  f!i 


^^^^^^^^^^^^^^^^^^^^^^^,■.^^^Y-|'.^^.^^^■■  ASWAW^W.',^  ,W1^  A'.  ^\pWiWml\sa^4l 


>Ls    t- 


-IRON  BASE  PLATE 
IENTS;  PLATE.  2>i" 
iNG  FLANGE  AND  Rl 
HICK 


X'METAL 


!i*  METAL 


INDEX. 


PAGE 

Accumulators 325,  326 

Acetic  acid 81 

Adamson  joints 225-227 

Air  for  combustion 58,  61 

dilution 61 

loss  from  excess 71 

per  pound  of  coal 63 

supply  for  boiler,  measurement  of 351 

A!my  boiler 33 

American  independently-fired  superheaters 44 

stoker 1 1  g 

Angle-valves 253 

Anthracite  coal 47 

Area  of  circles 4 '  4 

steam-pipe 207 

uptake 370 

Areas  of  segments  of  circles 412.  413 

Ash-pit 6 

doors 6 

Assembling  and  riveting  boilers 318 

Atmosphere,  composition  of 59 

Atomic  weight 55 

Attached  superheaters  .- 38 

Babcock   &  Wilcox  attached  superheater 38 

boiler 22 

Baird's  steam-trap 275 

Balancing  heat  in  boiler  test 358 

Belleville  boiler 28 

Belpaire  fire-box 20 

421 


422  IXDEX. 

PAGE 

Berryman  feed-water  heater 2S3 

Bituminous  coal 48 

Blow-off  pipes 286 

Blowing  out  brine 98 

Blue  heat 190 

Board  of  Trade,  rules  for  flues 235 

Boiler,  foundation  for 101 

selection  of  type  of 360 

settings  for  B.   &  W 105 

Dutch  oven 1 1 1 

cylindrical  tubular 102 

Heine 106 

marine  water-tube 107 

Stirling 106 

Boilers,  two-flue 6 

vertical 10-14. 

water-tube 20 

marine 27 

Yarrow 32 

Boiler  accessories 52 

design 360 

explosions 245 

front 6 

horse-power 1 48 

shop  plan  and  description  of 305 

testing,  evaporative ^^^ 

tubes,  size  and  surface  of 416 

Boring-mill 31  r 

Brackets 173,  391 

Brass 193 

Bridge-wall 2 

Brine,  loss  from  blowing  out 98 

Bronze 193 

Buck-staves 105 

Bumped  up  head 198 

Bundy  steam-trap 277 

bursting  pressure  of  fittings 295 

Butt-joint 202,  214,  216 

Calculation  of  gas  analysis 67 

riveted  joints 201 

stay-rods 385 

Calking 331 

Calorimeters  for  steam.  Carpenter 345 

Peabody 342 


INDEX. 


423 


PAGE 

Cam  and  toggle  riveting-machine 321 

Carbon,  heat  of  combustion  of 53,  54 

Carbonate  of  lime 78 

Cast  iron 191 

Chapman  valves 254 

Channel-bars,  calculation  of 386 

Charcoal 40 

Check-valves 256 

Chemistry  of  combustion 54 

Chimney,  area  of 136 

draught 134 

forms  of 136 

stability  of 138 

Chimneys 132 

Kent's  table 133 

Circles,  area  of 414 

circumference  of 414 

Circumference  of  circles 414 

Cleaning  fires 1 28 

Coal,  air  per  pound  of 63 

conveyer 302 

belt 1 . . .  302 

bucket 301 

bucket-filler 302 

distributor 302 

value  of 144 

volume  of  ton  of 74 

Coals,  anthracite 47 

bituminous 48 

caking,  bituminous 48 

dry  bituminous 48 

long-flaming  bituminous 48 

semi-bituminous 47 

Cold-water  test 332 

Collapsing  pressure 223 

Coke 48 

Combination 266 

Combustion,  air  required  f or  .     58 

chemistry  of 54 

heat  of 50-52,  56 

incomplete 70 

rate  of 149 

temperature  of 73 

volume  of  air  for 61 

Complex  stays 169 


424  INDEX. 

PAGE 

Composition 193 

of  atmosphere 59 

of  fuels 50,  51,  52 

Compression 1 83 

Conical  through  tubes 8 

Copper 192 

Cornish  boiler 8 

Corrosion 94 

Corrugated  furnace 227 

Covering  pipes,  saving  by 290 

Crane-lifts 309 

Crown-bars 10 

Crowfeet 157 

Crushing  of  plate 204 

rivet 204 

Curtis  separator 280 

steam-trap 277 

Cylinder,  end  tension  in 196 

rim  tension  in 197 

strength  of 196 

Cylindrical  tubular  boiler 2 

setting 102 

staying  of 1 54 

Damper  regulator 272 

Density  of  gases , 55 

Detachable  brackets 1 74 

Detroit  separator 280 

Diagram  for  setting  return  tubular  boilers 399 

Diameter  of  boiler 364 

rivet 205 

Diagonal  stays 195 

Down-draught  furnaces 1 23 

Draught  of  chimneys 134 

forced  and  induced 125 

gauge 349 

Howdens  system 127 

split 10 

wheel 9 

Drill  for  tube  holes 310 

Drilled  or  punched  plates 203 

Dry-pipe 171 

Du  Long's  formula 157 

Dudgeon  tube-expander 329 


INDEX. 


425 


PAOB 

Economizers 


sizes  of  Green's 


129 
407 


of  Sturtevant's 4o8,  409 

Efficiency  of  riveted  joints ; 2oi 

Elasticity,  modulus  of j82 

Elastic  limit 182 

Equivalent  evaporation 146 

Evaporative  test  of  boiler 152 

Excess  of  air,  loss  from ^  1 

Expanders  for  tubes 3,28,  329 

Expansion  pads 20 

Explosions  of  boilers 245 

Factor  of  safety 240,  366 

Farnley  furnace 228 

Feed-pipes 283 

pumps 284 

water  filter 87,  281 

Feed-water  heaters  (lime-extracting) 82 

Berryman 283 

Hoppes 82 

Wainwright 282 

impurities  in  (table) 76 

organic  impurities 91 

Filter,  feed-water 87,  281 

oil 281 

Finishing  flanges 311 

Fire  cracks 127 

doors 5 

engine  boiler 14 

tubes 236 

Firing 115 

Fittings,  bursting  pressure  of 295 

for  superheated  steam 46 

Flange-punch 309 

Flanging  heads 507 

Flat  plates 238 

Flow  of  steam , 298,  347 

Flue-gases 348 

Flues 221 

area  of ]  -<, 

collapsing,  pressure  of 223-235 

discussion  of  tests 2  ; } 

rules  for .  .    2^4 

strengthened 224 


426  INDEX. 

PAGE 

Flynn  steam-trap 276 

Forced  draught 125 

Forms  of  test-pieces 179,  186 

Foster's  independently-fired  superheater 43 

Foundation  for  boilers 101 

Foundation  ring 10 

Fox's  corrugated  furnace 227 

Friction  of  riveted  joints 204 

Fuel,  artificial 49 

standard 143 

Fuels,  composition  of 50,  51,  52 

Furnace,  corrugated 227-233 

Dutch  oven 43,  101 

Farnley's 228 

flues,  tests  of 223 

Hawley  down-draught 1 24 

Holmes' 229 

Morison's „ 232 

mouth 167 

Purve's 232 

Furnaces 107 

down-draught 1 23 

oil-burning 1 24 

Fusible  plugs 270 

Galvanic  action 87 

Gas  analysis,  calculation  of 67 

apparatus,  Orsat's 64 

natural 49 

Galloway  boiler 8 

G  irders 236 

Globe  valves 252 

Grate-area 362 

bars 112 

water 1 24 

Grates,  rocking 114 

Green's  economizer 130,  131 

link  grate 122 

Grooving 95 

Gun  iron 191 

Gusset  stays 169,  196 

Hand-holes 5.  38° 

Hand-riveting 327 

Hangers  for  pipe 296 


INDEX.  427 

PAGE 

Hawley  down-draught  furnace 1  24 

Heat-balance  in  boiler  test 358 

Heat  of  combustion 50,  51,  52,  56 

(carbon)  .  .    53.  ^4 

calculation  of 56 

(fuels) 51 

of  the  liquid  (water) 418 

Heating-surface 6 

of  boiler-tubes  (table) 410 

value  of 1 50 

Heine  attached  superheater 39 

boiler 24 

Holmes'  furnace 229 

Hollow  cylinder 196 

Hoppe's  purifier 82 

Horizontal  multitubular  boiler 2 

Horse-power  of  boilers 148 

Howden's  system 127 

Huston  brace 160 

Hydraulic  accumulators 325,  326 

riveting-machine 321 

with  cam  and  toggle ^26 

test 232 

of  boiler 240 

Incomplete  combustion,  loss  from -o 

Independently-fired  superheaters 42 

Induced  draughts 125 

Injectors 285 

Iron  rods,  weight  of 415 

Joints  in  piping 205 

Jones'  under-fed  stoker 1 22 

Kent's  table  of  chimneys j  3- 

Kerosene  oil 04 

Koerting  injector 285 

Laminations tgg 

Lancashire  boiler - 

LaP 204,  374 

Lap-joints 20  5 

with  welt 209,  211 

-seam  boilers 250 


428  INDEX. 

PAGE 

Laying  out  plates 311 

stays 383 

Leavitt  boiler 20 

Length  of  sections 379 

Lever  safety-valve 259 

Lewes  (marine-boiler  scale) 84 

Liberty  tube-cleaner 299 

Life  of  boilers 246 

Lifting-dogs 308 

Lignite 48 

Lime-extracting  feed-water  heater 82 

Limit  of  elasticity 182 

Link  grate,  Green's 122 

Lloyd's  rules  for  flues 235 

Locke  damper  regulator 272 

Xocomotive-boiler 18 

staying  of 162 

type 20 

Logarithms 410 

Longitudinal  joint 368 

Mahler's  composition  of  fuels " 52 

formula 58 

Malleable  iron 192 

Manholes 5,  172,  380 

Manning  boilers 10,  n 

Marine  boilers 15,  27 

Babcock  &  Wilcox 27 

proportions  of 151 

scale 84-89 

staying  of 167 

water-tube 27 

Materials 1 7S 

McDaniels  trap 274 

Mechanical  stokers 116 

American 1 1  o 

Jones' 1  20 

Roney 117 

Methods  of  failure  of  riveted  joints 202 

of  making  boiler  tests ^t,^ 

of  supporting  boilers 173 

of  testing  plate 1S0,  186 

Mineral  impurities 7; 

matter  in  water  (table) 7  5 

oil 40 


INDEX. 


429 


Modulus  of  elasticity jg2 

Morison's  furnace 232 

Natural  sines,  cos,  and  tan 4x4 

trigonometric  functions 414 

Naval  boilers,  proportions  of 151 

Nozzles 380 

<  >il-burning  furnaces 124 

filter 28r 

scale 89 

Organic  impurities  in  feed-water OI 

Orsat's  gas  apparatus 64 

Pancake 89 

Peat 48 

Peet  valve 255 

Petroleums,  composition  of 50 

Pipe,  anchor  for 296' 

arrangement  of  steam 288-297 

area  and  size  of Appendix 

blow-off 286 

feed 283 

hangers  for 296 

size  for  given  horse-power 297 

support  for 296 

Pipe-bends,  rigidity  of 292 

covering 299 

fittings  for  superheated  steam 46 

joints 295 

Piping 288 

Pitch  of  rivets 205 

Pitting 95 

Plain  cylindrical  boiler , 7 

Plan  of  boiler-shop 305 

Planing-machine ^14 

plates 314 

Plate,  crushing  of 204 

lap    204 

Planer 3*5 

rolls 314 

shearing  of 204 

tearing  of 203 

Pop  safety-valve 263 

Portable  riveting-machine ^23 


•13° 


IXDEX. 


PAGE 

Power  of  boilers 1 43 

Power-pump  for  riveter 324 

Priming  .     373 

Proportions  of  boilers I51    « 

Properties  of  saturated  s^eam 419 

of  steel 184 

Prosser  tube-expander 328 

Pulsation  of  steam-pipes 295 

Pumps 284 

Pump  for  hydraulic  riveter 324 

Punch 3i4 

and  holder 3ID 

for  tube-holes  .  .  . 3IC 

Punched  or  drilled  plates 203,  319 

Purve's  furnace 230,  231 

Pyrometers 35° 

Rate  of  combustion 149 

Reach  of  a  riveting-machine - 322 

Reducing-val  ve 27 l 

Reduction  of  area 183 

Return  steam-traps 277 

Rigidity  of  pipe-bends 292 

Ring-seam 373 

Rivet,  diameter  of 205 

Riveted  joints,  calculation  of 201 

designing 217 

efficiency  of 201 

friction  of 204 

limitations 221 

methods  of  failure -  -  -    202 

Riveting-machines,  cam  and  toggle 321 

hydraulic 321 

with  cam  and  toggle 326 

portable 323 

Rivets *9X>  *99>  200 

pitch  of 205 

shearing  and  crushing 204 

Rocking-grates 114 

Rol.ls  for  plate 3  J4 

Roney  stoker 117 

Safety-plugs 270 

valves 257 

Sal-ammoniac Si 


I. XL)  EX. 


431 


PAGE 

Sample  boiler  test  blank --, 

Saving  by  covering  pipes 2gu 

Si  ale,  marine  boiler 84   80 

Starling , ,  4 

Scutch  boiler 1  -    ,  - 

Screw-threat  Is  (table) 4,5 

Sea-water,  composition  of 3. 

Segments  of  circles 4u>  ^,  - 

Selection  of  type  of  boiler ji    ^uo 

Semi-bituminous  coal ^ 

Separator,  Curtis 280 

Detroit 28 1 

Stratton 270 

Triumph 280 

Shearing 183 

of  rive  ts 204 

plates 204,  313 

Shears ^ 

Shop-practice ^04 

Size  and  surface  of  boiler-tubes 4X6 

of  steam-pipe 297 

Sizes  of  steam,  gas,  and  water  pipe  1  table  I 41  - 

Smoke-box 6 

prevention l22 

Snap-riveting ^27 

Soda -S 

Specific  heat 55 

of  superheated  steam 5*    »8 


volumes 


55 


Specifications  and  contract  for  boiler ^>q2,  ^94 

for  steel ^4 

Sphere,  strength  of I08 

Spherical  ends 1 70 

Split-draught 10 

Stability  of  chimneys 138 

Stay-bolts 103 

Stay-rods 1 94,  385 

calculation  of 385 

Stayed  flat  plates 238 

Staying  1 53,  381 

beneath  tubes 1 60 

(calculation  of) " 381 

cylindrical  tubular  boiler 1  ^3 

laying  out 383 

locomotive-boiler 162 


432  IXDEX. 

PACE 

Staying  of  marine  boiler *68 

Stays,  diagonal 195 

Steam-dome 170 

Steam,  flow  in  pipes 298 

flow  of 298,  347 

gas,  and  water  pipe  (table) 417 


gauges . .  . 


268 


nozzle 172 

piping 288,  297 

quality  of 1 44 

space 145 

tables 419 

traps,  Baird's 275 

Bundy 277 

Curtis 277 

Flynn 276 

McDaniel's 214 

return 277 

Walworth 275 

Steam-pipe  pulsations 2Q5 

Steel 184 

specifications  for 184 

Stirling  attached  superheater 30 

boiler 25 

Stokers,  mechanical 116 

Strain 182 

Stratton  separator 279 

Strength  of  boilers 1 78 

Stress .- 1S2 

Stretch  limit 1S2 

Submerged  tube-sheet - 13,  14 

Sulphate  of  lime 78 

Sunken  tube-sheet 13,  14 

Superheated  steam,  specific  heat  of 38 

Superheaters 37 

American 44 

attached 38 

Babcock  &  Wilcox 38 

Foster 43 

Heine 39 

independently-fired 42 

Stirling 39 

Superheating  surface,  Manning  boiler 13 

Surface  blow 92 


INDEX.  a--, 

r.\<.E 

Tabic  of  logarithms . IO 

Tables  of  properties  of  saturated  steam 4 ,  t. 

Tannic  acid gr 

Tearing  of  plate 20, 

Temperature  of  combustion -, 

Test  on  furnace  flues 22*5-2^ 

Testing  boilers  for  evaporation 

Testing-machines ,  -  g 

Test-pieces j  -q 

Testing  plate,  methods  of jgo  tg0 

Thickness  of  shell -.„g 

Thornycroft  boiler .<-> 

Throttling  calorimeter ,  ,  2 

Through-stays 2 

Traveling  grate I22 

Triumph  separator 2g0 

Tube-cleaner  for  soot ^OI 

Tube-cleaners,  Liberty 20q 

Weinland ^00 

Tube-expanders •-,  2g 

Tube-holes,  drills  for ,IO 

punch  for -,  IO 

plates 2 

sheet 362,  376 

sheet,  sunken r»    T , 

Tubes 302 

after  expanding -  ,0 

Two-flue  boiler 6 

Type  of  boiler,  selection  of **,  ,00 

Ultimate  elongation jg, 

strength ,Sj 

Uptake 2 

areaof 379 

U.  S.  Inspectors'  rules  for  flues 2 . , 

Valves 2^2 

angle 2  =; ; 

Chapman 2^4 

check 256 

gate 25J 

globe :;: 

Peet 255 

reducing 271 


434  INDEX. 

PAGE 

Valves,  safety,  lever 259 

P°P 263 

Van  Stone  joint 295 

Vertical  boilers 10-14 

rolls  for  plate 317 

Vibration  of  steam  pipes 295 

Volume  of  ton  of  coal 74 

Volumes,  specific 55 

Wainwright  feed-water  heater 282 

Walworth  steam-trap 275 

Wash-out  plugs 173 

Water  column 266 

grate 124 

heat  of  the  liquid 418 

leg 18 

level 365 

tube  boilers 20 

boiler-setting 105,  106 

marine  boilers 27 

weight  and  volume  of  (table) 418 

Weinland  tube-c  leaner 300 

Wheel-draught 9 

William's  composition  of  fuels 51 

Wind  pressure 138 

Wood 49 

Wrought  iron 190 

steam,  gas.  and  water  pipe 4*7 

Yarrow  boiler 32 

Yield-point 182 

Zinc  in  boilers 87 


Short-title  Catalogue 

OF    THE 

PUBLICATIONS 

OF 

JOHN  WILEY   &  SONS 

New  York 

London:   CHAPMAN    &  HALL,  Limited 


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